GeoPort
Encyclopedia
GeoPort was a serial data
system used on some models of the Apple Macintosh. GeoPort slightly modified the existing Mac serial port
pins to allow the computer's internal sound hardware to emulate various devices such as modem
s and fax machines. GeoPort could be found on late-model m68k-based machines (the AV series) as well as many pre-USB Power Macintosh
models. Some later Macintosh models also included an internal GeoPort known as the Communications Slot. Apple GeoPort technology is now obsolete, and modem support is typically offered through USB
.
team were working on the design of a local area network
ing system known as "AppleNet", based on the Xerox XNS protocol stack running at 1 Mbit/s. There were also plans to offer AppleNet on the Apple II
. Mac development had been ongoing for some time at this point, but the $500 price of AppleNet led Steve Jobs
to refuse its inclusion on the low-cost machine. The Macintosh engineers did manage to make some room for a "peripheral bus" instead, using the $5 Zilog 8530 "Serial Communications Controller" (SCC) instead of the more common, and almost free, UARTs that were used on most designs of the era.
The SCC drove two ports and could be operated in either of two modes, RS-232
mode at 12 V, or RS-422 mode at 5 V using pairs of wires supporting differential signaling
. In the former mode the ports operated like the serial ports on any contemporary computer, and, with an appropriate cable, could be used with any common serial device, like modem
s. In the latter 5 volt mode, the SCC could operate at speed up to 250 kbit/s, which was put to use driving the ImageWriter
series of printers and some other devices. On the Macintosh, one of the SCC's ports was labeled "modem" and the other "printer", although there was no logical difference between the two.
Given the poor sales of the Lisa system, development efforts on that project were dramatically scaled back in September 1983 in favor of the Macintosh. AppleNet for both the Lisa and Apple II became a casualty in October. Cancellation of AppleNet gave the vague plans for a peripheral bus new importance, briefly becoming "AppleBus". Gursharan Sidhu led development of what eventually developed into AppleTalk
and its associated LocalTalk
hardware, developing a truly "Mac-like" plug-n-play networking system running at 230 kbit/s.
AppleTalk allowed for relatively high speeds because its packetized nature allowed the CPU to send blocks of data to the port at high speed when it wasn't busy doing something else. In this case the speeds were primarily a function of the internal clocks in the SCC. A number of vendors provided network connectors with their own clocks that ran at much higher speeds, up to 1 Mbit/s. A lack of standardization precluded these from becoming common.
Since both serial ports were driven by the single SCC, and those in turn by software drivers running on the CPU, the CPU's load could dramatically affect throughput. Using LocalTalk and the serial port at the same time generally halved the performance of the latter. Apple was aware of these problems, and starting with the Macintosh IIfx
they attempted to address them by including two dedicated "Input/Output Processors" (IOP), customized MOS 6502s running at 10 MHz. The IOPs offloaded the low-level driver code from the host CPU, running the floppy disks and serial ports, only interrupting the CPU when there was data to transfer. The IIfx also introduced a DMA
mode for the SCSI
-bus, but this was not available for use by the IOPs. The IOPs also appeared on the Quadra 900 and Quadra 950.
s (DSP) in the "AV" series machines. The DSP was primarily intended to offer audio and video digitization support, accessed though the custom 60-pin "Digital Audio/Video" (DAV) port on the rear of the machines. However, there was also the possibility of using the DSP to emulate a modem
, another common task for DSPs. Using the relatively advanced 3210 would offer higher performance than existing modems, which used lower-end DSPs, and much better performance than softmodem
s using the host CPU.
In order to support this mode of operation, the serial ports would have to operate at high enough speeds to allow the DSP to send the signal, in digital form, to an external analog to digital converter, or "line adapter" as it was referred to in Apple terminology. To operate at these speeds, as well as handle the higher voltages and powers of the phone system, the adapter needed to have a separate power source. Apple solved this problem by shoehorning in a 9th pin to the existing 8-pin Mini-DIN connector
. The result was GeoPort.
In GeoPort mode the SCC was placed in a high-speed mode using external clocking, similar to the earlier high-performance LocalTalk replacements. The DSP then generated signals and sent them over the serial bus to the adapter, which converted them to analog and amplified them to telephone levels. In GeoPort mode, speeds up to 2 Mbit/s were supported.
The only widely known device to make use of the GeoPort was Apple's own "GeoPort Telecom Adapter". Initially released as the "pod" with the AV Macs in 1993, it later became its own separate product in early 1995, when it was released for PowerPC-based Macintosh machines that did not include AV-related hardware out of the box. The Adaptor eventually came in three versions, an internal model that plugged into the Communication Slot II (CS II), and two external versions (the GeoPort Telecom Adapter and the GeoPort Telecom Adapter II) all providing a standard RJ-11 phone line connector. The CS II was essentially an internal GeoPort with various other signals as well. Initially the adapter driver software could support speeds up to 9600 bit/s, but later upgrades introduced full V.34 compliance, running at up to 33.6 kbit/s. In practice the GeoPort Adaptors tied up huge amounts of CPU time, and led to performance problems throughout the system. They were also notorious for poor quality connections, dropped calls and poor support from existing software; many pundits recommended not using them.
SAGEM also introduced an ISDN adaptor for GeoPort, the "Planet-ISDN Geoport Adapter", or SPIGA, which they now sell in a USB version. Global Village also produced a variant of its compact Teleport Modems for Apple Performas and third-party Mac computers that used the 9th pin to supply power, but these were true hardware modems.
, although they were all based on their own standards, typically connected to the computers via a serial port at relatively low speeds. Although these signals could have been routed using existing networking standards like Ethernet
, most companies used custom systems, like Switch56
.
Apple started an effort to promote GeoPort as a standardized computer interface to PBX systems. They envisioned different GeoPort adapters for different back-end systems; a Switch56 interface could be used with Northern Telecom systems, while another would be used to connect to the InteCom switches that Apple used. Apple claimed that the "same GeoPort phone pod will be able to support TAPI
applications on a Windows PC and Telephone Manager applications on a Mac."
To connect those systems to the Macintosh, in particular, Apple created the Macintosh Telephony Architecture (MTA) and promoted it as a standarized telephony application program interface. The MTA consisted primarily of three parts, the "Telephone Manager" which handled call-control, the "Telephone Tool" that mapped Telephone Manager commands onto specific hardware, and finally a set of telephony-related Apple Events
that would allow simpler operation from any Macintosh system. MTA was essentially Apple's analog of Microsoft's TAPI or Novell's TSAPI.
To promote the system, in late 1994 Apple organized the Versit alliance along with AT&T
, IBM
and Siemens
to attempt to standardize the commands that the PBX systems responded to. Novell announced that they would adapt TSAPI to work on top of the Versit standards. All of these efforts were hampered by a lack of standardization among PBX vendors, and their lack of real support for GeoPort adapters.
After two years of effort with little to show for it, Apple eventually gave up on Versit, and telephony in general. The main problem was that the various PBX companies relied on vendor lock-in
to keep their existing customers coming back to them for newer products, so the very concept of a standardized system was seen as a problem rather than a solution. Additionally there was no support for high-speed serial on the basic PC, so users would have to buy an add-on card if they were going to use GeoPort, at which point it made just as much sense to buy a custom adaptor on a different card.
The GeoPort was dropped, along with SCSI
and ADB
, when Apple introduced the iMac
in 1998; early demonstration models had a software modem based on the GeoPort Telecom Adapter’s technology, but this was replaced with a hardware 56K modem by the time the iMac shipped.
) and RS-232 modes.
Pin # GeoPort RS-422 RS-232 Name
1 SCLK HSKo DTR Serial Clock (out), Handshake Out, Data Terminal Ready
2 SCLK HSKi DSR Serial Clock (in), Handshake In, Data Set Ready
3 TxD- TxD- TD Transmit data (-ve signal)
4 GND GND GND Cable ground
5 RxD- RxD- RD Receive data (-ve signal)
6 TxD+ TxD+ Transmit data (+ve signal)
7 TxHS GPi CD Wakeup/DMA Request, General Purpose input, Carrier Detect
8 RxD+ RxD+ (ground) Receive data (+ve signal)
9 +5 V Power, 350 mA maximum
Serial communications
In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...
system used on some models of the Apple Macintosh. GeoPort slightly modified the existing Mac serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
pins to allow the computer's internal sound hardware to emulate various devices such as modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s and fax machines. GeoPort could be found on late-model m68k-based machines (the AV series) as well as many pre-USB Power Macintosh
Power Macintosh
Power Macintosh, later Power Mac, was a line of Apple Macintosh workstation-class personal computers based on various models of PowerPC microprocessors that were developed, marketed, and supported by Apple Inc. from March 1994 until August 2006. The first models were the Power Macintosh 6100,...
models. Some later Macintosh models also included an internal GeoPort known as the Communications Slot. Apple GeoPort technology is now obsolete, and modem support is typically offered through USB
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
.
AppleBus
Prior to the introduction of the Apple Macintosh, Apple engineers on the Apple LisaApple Lisa
The Apple Lisa—also known as the Lisa—is a :personal computer designed by Apple Computer, Inc. during the early 1980s....
team were working on the design of a local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
ing system known as "AppleNet", based on the Xerox XNS protocol stack running at 1 Mbit/s. There were also plans to offer AppleNet on the Apple II
Apple II
The Apple II is an 8-bit home computer, one of the first highly successful mass-produced microcomputer products, designed primarily by Steve Wozniak, manufactured by Apple Computer and introduced in 1977...
. Mac development had been ongoing for some time at this point, but the $500 price of AppleNet led Steve Jobs
Steve Jobs
Steven Paul Jobs was an American businessman and inventor widely recognized as a charismatic pioneer of the personal computer revolution. He was co-founder, chairman, and chief executive officer of Apple Inc...
to refuse its inclusion on the low-cost machine. The Macintosh engineers did manage to make some room for a "peripheral bus" instead, using the $5 Zilog 8530 "Serial Communications Controller" (SCC) instead of the more common, and almost free, UARTs that were used on most designs of the era.
The SCC drove two ports and could be operated in either of two modes, RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
mode at 12 V, or RS-422 mode at 5 V using pairs of wires supporting differential signaling
Differential signaling
Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...
. In the former mode the ports operated like the serial ports on any contemporary computer, and, with an appropriate cable, could be used with any common serial device, like modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s. In the latter 5 volt mode, the SCC could operate at speed up to 250 kbit/s, which was put to use driving the ImageWriter
ImageWriter
The ImageWriter was a product line of dot matrix printers manufactured by Apple Computer's and designed to be compatible with their entire line of computers...
series of printers and some other devices. On the Macintosh, one of the SCC's ports was labeled "modem" and the other "printer", although there was no logical difference between the two.
Given the poor sales of the Lisa system, development efforts on that project were dramatically scaled back in September 1983 in favor of the Macintosh. AppleNet for both the Lisa and Apple II became a casualty in October. Cancellation of AppleNet gave the vague plans for a peripheral bus new importance, briefly becoming "AppleBus". Gursharan Sidhu led development of what eventually developed into AppleTalk
AppleTalk
AppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
and its associated LocalTalk
LocalTalk
LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s...
hardware, developing a truly "Mac-like" plug-n-play networking system running at 230 kbit/s.
Performance issues
Although the SCC's internal clocks supported any transmission speed up to 250 kbit/s, in practice these sorts of speeds were rarely obtainable. Data was provided to the SCC by the host CPU, which was also loaded down with other tasks. In RS-232 mode more constant polling was needed, and the best expected performance varied from 9600 bit/s on the Mac Plus, to 115,200 bit/s on later machines.AppleTalk allowed for relatively high speeds because its packetized nature allowed the CPU to send blocks of data to the port at high speed when it wasn't busy doing something else. In this case the speeds were primarily a function of the internal clocks in the SCC. A number of vendors provided network connectors with their own clocks that ran at much higher speeds, up to 1 Mbit/s. A lack of standardization precluded these from becoming common.
Since both serial ports were driven by the single SCC, and those in turn by software drivers running on the CPU, the CPU's load could dramatically affect throughput. Using LocalTalk and the serial port at the same time generally halved the performance of the latter. Apple was aware of these problems, and starting with the Macintosh IIfx
Macintosh IIfx
The Macintosh IIfx was a model of Apple Macintosh computer, introduced in 1990 and discontinued in 1992. At introduction it cost from US $9,000 to US $12,000, depending on configuration, and was the fastest Mac...
they attempted to address them by including two dedicated "Input/Output Processors" (IOP), customized MOS 6502s running at 10 MHz. The IOPs offloaded the low-level driver code from the host CPU, running the floppy disks and serial ports, only interrupting the CPU when there was data to transfer. The IIfx also introduced a DMA
Direct memory access
Direct memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....
mode for the SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
-bus, but this was not available for use by the IOPs. The IOPs also appeared on the Quadra 900 and Quadra 950.
AV and GeoPort
After the early Quadra machines, Apple started a short-lived experiment including AT&T 3210 digital signal processorDigital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
s (DSP) in the "AV" series machines. The DSP was primarily intended to offer audio and video digitization support, accessed though the custom 60-pin "Digital Audio/Video" (DAV) port on the rear of the machines. However, there was also the possibility of using the DSP to emulate a modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, another common task for DSPs. Using the relatively advanced 3210 would offer higher performance than existing modems, which used lower-end DSPs, and much better performance than softmodem
Softmodem
A Softmodem, or software modem, is a modem with minimal hardware capacities, designed to use a host computer's resources to perform most of the tasks performed by dedicated hardware in a traditional modem.A Softmodem is also referred to as a Winmodem because the first commercially available...
s using the host CPU.
In order to support this mode of operation, the serial ports would have to operate at high enough speeds to allow the DSP to send the signal, in digital form, to an external analog to digital converter, or "line adapter" as it was referred to in Apple terminology. To operate at these speeds, as well as handle the higher voltages and powers of the phone system, the adapter needed to have a separate power source. Apple solved this problem by shoehorning in a 9th pin to the existing 8-pin Mini-DIN connector
Mini-DIN connector
The mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
. The result was GeoPort.
In GeoPort mode the SCC was placed in a high-speed mode using external clocking, similar to the earlier high-performance LocalTalk replacements. The DSP then generated signals and sent them over the serial bus to the adapter, which converted them to analog and amplified them to telephone levels. In GeoPort mode, speeds up to 2 Mbit/s were supported.
The only widely known device to make use of the GeoPort was Apple's own "GeoPort Telecom Adapter". Initially released as the "pod" with the AV Macs in 1993, it later became its own separate product in early 1995, when it was released for PowerPC-based Macintosh machines that did not include AV-related hardware out of the box. The Adaptor eventually came in three versions, an internal model that plugged into the Communication Slot II (CS II), and two external versions (the GeoPort Telecom Adapter and the GeoPort Telecom Adapter II) all providing a standard RJ-11 phone line connector. The CS II was essentially an internal GeoPort with various other signals as well. Initially the adapter driver software could support speeds up to 9600 bit/s, but later upgrades introduced full V.34 compliance, running at up to 33.6 kbit/s. In practice the GeoPort Adaptors tied up huge amounts of CPU time, and led to performance problems throughout the system. They were also notorious for poor quality connections, dropped calls and poor support from existing software; many pundits recommended not using them.
SAGEM also introduced an ISDN adaptor for GeoPort, the "Planet-ISDN Geoport Adapter", or SPIGA, which they now sell in a USB version. Global Village also produced a variant of its compact Teleport Modems for Apple Performas and third-party Mac computers that used the 9th pin to supply power, but these were true hardware modems.
As a "standard"
During the evolution of GeoPort, the telecommunications market was undergoing major changes with the introduction of newer all-digital PBX systems. A number of these companies offered some sort of computer telephony integrationComputer telephony integration
Computer telephony integration, also called computer–telephone integration or CTI, is a common name for any technology that allows interactions on a telephone and a computer to be integrated or coordinated...
, although they were all based on their own standards, typically connected to the computers via a serial port at relatively low speeds. Although these signals could have been routed using existing networking standards like Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
, most companies used custom systems, like Switch56
Switch56
Nortel's Switch56 was a networking protocol built on top of the telephone cabling hardware of their Digital Multiplex System and other telephone switches....
.
Apple started an effort to promote GeoPort as a standardized computer interface to PBX systems. They envisioned different GeoPort adapters for different back-end systems; a Switch56 interface could be used with Northern Telecom systems, while another would be used to connect to the InteCom switches that Apple used. Apple claimed that the "same GeoPort phone pod will be able to support TAPI
Telephony Application Programming Interface
The Telephony Application Programming Interface is a Microsoft Windows API, which provides computer telephony integration and enables PCs running Microsoft Windows to use telephone services. Different versions of TAPI are available on different versions of Windows...
applications on a Windows PC and Telephone Manager applications on a Mac."
To connect those systems to the Macintosh, in particular, Apple created the Macintosh Telephony Architecture (MTA) and promoted it as a standarized telephony application program interface. The MTA consisted primarily of three parts, the "Telephone Manager" which handled call-control, the "Telephone Tool" that mapped Telephone Manager commands onto specific hardware, and finally a set of telephony-related Apple Events
Apple events
Apple events are the canonical message-based interprocess communication mechanism in Mac OS, first appearing in System 7 and supported by every version since then, including Mac OS X. Apple events describe "high-level" events such as "open document" or "print file", whereas earlier OS's had...
that would allow simpler operation from any Macintosh system. MTA was essentially Apple's analog of Microsoft's TAPI or Novell's TSAPI.
To promote the system, in late 1994 Apple organized the Versit alliance along with AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
, IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
and Siemens
Siemens
Siemens may refer toSiemens, a German family name carried by generations of telecommunications industrialists, including:* Werner von Siemens , inventor, founder of Siemens AG...
to attempt to standardize the commands that the PBX systems responded to. Novell announced that they would adapt TSAPI to work on top of the Versit standards. All of these efforts were hampered by a lack of standardization among PBX vendors, and their lack of real support for GeoPort adapters.
After two years of effort with little to show for it, Apple eventually gave up on Versit, and telephony in general. The main problem was that the various PBX companies relied on vendor lock-in
Vendor lock-in
In economics, vendor lock-in, also known as proprietary lock-in or customer lock-in, makes a customer dependent on a vendor for products and services, unable to use another vendor without substantial switching costs...
to keep their existing customers coming back to them for newer products, so the very concept of a standardized system was seen as a problem rather than a solution. Additionally there was no support for high-speed serial on the basic PC, so users would have to buy an add-on card if they were going to use GeoPort, at which point it made just as much sense to buy a custom adaptor on a different card.
The GeoPort was dropped, along with SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
and ADB
Apple Desktop Bus
Apple Desktop Bus is an obsolete bit-serial computer bus connecting low-speed devices to computers. Used primarily on the Macintosh platform, ADB equipment is still available but not supported by most Apple hardware manufactured since 1999....
, when Apple introduced the iMac
IMac
The iMac is a range of all-in-one Macintosh desktop computers built by Apple. It has been the primary part of Apple's consumer desktop offerings since its introduction in 1998, and has evolved through five distinct forms....
in 1998; early demonstration models had a software modem based on the GeoPort Telecom Adapter’s technology, but this was replaced with a hardware 56K modem by the time the iMac shipped.
Pinouts
The table below shows the name and purpose of the various pins in the GeoPort-enabled serial connector when used in GeoPort, RS-422 (LocalTalkLocalTalk
LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s...
) and RS-232 modes.
Pin # GeoPort RS-422 RS-232 Name
1 SCLK HSKo DTR Serial Clock (out), Handshake Out, Data Terminal Ready
2 SCLK HSKi DSR Serial Clock (in), Handshake In, Data Set Ready
3 TxD- TxD- TD Transmit data (-ve signal)
4 GND GND GND Cable ground
5 RxD- RxD- RD Receive data (-ve signal)
6 TxD+ TxD+ Transmit data (+ve signal)
7 TxHS GPi CD Wakeup/DMA Request, General Purpose input, Carrier Detect
8 RxD+ RxD+ (ground) Receive data (+ve signal)
9 +5 V Power, 350 mA maximum