Freescale S08
Encyclopedia
The 9S08 is a 8-bit
microcontroller
(µC) family originally from Motorola
, now produced by Freescale Semiconductor
, descended from the Motorola 6800
microprocessor. It is a CISC
microcontroller. The 9S08 devices are more powerful and usually less expensive than the aging 68HC05
microcontrollers, and are found in almost any type of embedded systems. The larger members offer up to 128KB of paged flash
, and 8KB of RAM
. The paging scheme used allows for a theoretical maximum of 4MB of flash.
Internally, the 9S08 instruction set
is upward compatible with the 6805, with the addition of stack
indexed addressing mode
s. (Instructions using the SP register
have opcode
s prefixed with the byte 0x9E). It has a single eight-bit accumulator
, A, one eight-bit index register
, X, or one sixteen-bit index registers, HX (formed from the combination of H and X registers), a condition code register, a 16-bit
stack pointer, and a program counter
. For compatibility with the 6805 which does not have an H register, the most significant byte of the HX register, H, is cleared during reset, and H is the only register not stacked automatically when entering any ISR (Interrupt Service Routine
). Some instructions treat the H and X registers as a combined 16-bit HX register. Unlike the 6805, the stack can be placed anywhere in memory using appropriate instructions.
The standard method of programming or debugging the 9S08 family is via a standard 6-pin BDM
interface (only one pin is used for communication with the microcontroller).
A wide variety of peripherals is available for different members and/or packages. SCI, SPI, 10-bit or 12-bit A/D, (C)PWM, Input Captures are common with most members, but no external bus is available.
8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...
microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
(µC) family originally from Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
, now produced by Freescale Semiconductor
Freescale Semiconductor
Freescale Semiconductor, Inc. is a producer and designer of embedded hardware, with 17 billion semiconductor chips in use around the world. The company focuses on the automotive, consumer, industrial and networking markets with its product portfolio including microprocessors, microcontrollers,...
, descended from the Motorola 6800
Motorola 6800
The 6800 was an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System that also included serial and parallel interface ICs, RAM, ROM and other support chips...
microprocessor. It is a CISC
Complex instruction set computer
A complex instruction set computer , is a computer where single instructions can execute several low-level operations and/or are capable of multi-step operations or addressing modes within single instructions...
microcontroller. The 9S08 devices are more powerful and usually less expensive than the aging 68HC05
Motorola 68HC05
The 68HC05 is a broad family of 8-bit microcontrollers from Freescale Semiconductor .Like all Motorola processors that share lineage from the 6800, they use the von Neumann architecture as well as memory-mapped I/O. This family has five CPU registers that are not part of the memory...
microcontrollers, and are found in almost any type of embedded systems. The larger members offer up to 128KB of paged flash
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
, and 8KB of RAM
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
. The paging scheme used allows for a theoretical maximum of 4MB of flash.
Internally, the 9S08 instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
is upward compatible with the 6805, with the addition of stack
Call stack
In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, control stack, run-time stack, or machine stack, and is often shortened to just "the stack"...
indexed addressing mode
Addressing mode
Addressing modes are an aspect of the instruction set architecture in most central processing unit designs. The various addressing modes that are defined in a given instruction set architecture define how machine language instructions in that architecture identify the operand of each instruction...
s. (Instructions using the SP register
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
have opcode
Opcode
In computer science engineering, an opcode is the portion of a machine language instruction that specifies the operation to be performed. Their specification and format are laid out in the instruction set architecture of the processor in question...
s prefixed with the byte 0x9E). It has a single eight-bit accumulator
Accumulator (computing)
In a computer's central processing unit , an accumulator is a register in which intermediate arithmetic and logic results are stored. Without a register like an accumulator, it would be necessary to write the result of each calculation to main memory, perhaps only to be read right back again for...
, A, one eight-bit index register
Index register
An index registerCommonly known as a B-line in early British computers. in a computer's CPU is a processor register used for modifying operand addresses during the run of a program, typically for doing vector/array operations...
, X, or one sixteen-bit index registers, HX (formed from the combination of H and X registers), a condition code register, a 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
stack pointer, and a program counter
Program counter
The program counter , commonly called the instruction pointer in Intel x86 microprocessors, and sometimes called the instruction address register, or just part of the instruction sequencer in some computers, is a processor register that indicates where the computer is in its instruction sequence...
. For compatibility with the 6805 which does not have an H register, the most significant byte of the HX register, H, is cleared during reset, and H is the only register not stacked automatically when entering any ISR (Interrupt Service Routine
Interrupt handler
An interrupt handler, also known as an interrupt service routine , is a callback subroutine in microcontroller firmware, operating system or device driver whose execution is triggered by the reception of an interrupt...
). Some instructions treat the H and X registers as a combined 16-bit HX register. Unlike the 6805, the stack can be placed anywhere in memory using appropriate instructions.
The standard method of programming or debugging the 9S08 family is via a standard 6-pin BDM
Background Debug Mode interface
Background Debug Mode interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers...
interface (only one pin is used for communication with the microcontroller).
A wide variety of peripherals is available for different members and/or packages. SCI, SPI, 10-bit or 12-bit A/D, (C)PWM, Input Captures are common with most members, but no external bus is available.