AN910 Datasheet, PDF (35/51 Pages) STMicroelectronics – ST7 AND ST9 PERFORMANCE BENCHMARKING

ST7 AND ST9 PERFORMANCE BENCHMARKING
7.3.8 68HC08 MCU core
Programming model
Accumulator
- one 8-bit accumulator
- one 16-bit index register
- other registers
16-bit program counter
16-bit stack pointer
condition code register
LDA #8, X
ADD #A0
Instruction set
Cisc encoding
- CPI
1 cycle to 9 cycles
- average CPI
between 4 and 5 cycles
- IL
1 byte to 4 bytes
- average IL
between 2 and 3 bytes
- special addressing modes
indexed with 8-bit offset and post-increment
stack pointer relative (8/16-bit offset)
- special instructions
compare & branch like
decrement & branch like
memory-to-memory moves
direct to direct
direct ↔ indexed with post-increment
68HC08 CPU
Cpu internal buses
16-bit address bus, 8-bit data bus
(to be confirmed)
Instruction processing
Prefetch mechanism
- 1-byte queue
opcode lookahead register
Arithmetic Logic Unit
+/x
8-bit datapath
- 8-bit operations
- special functions
8x8 unsigned multiplication
16/8 unsigned integer division
5 cycles
7 cycles
On-chip/Off-chip buses
- on-chip buses
16-bit address bus
8-bit data/program memory bus
- off-chip buses
8/16-bit address bus
up to 22-bit with memory expansion module
8-bit data/program memory bus
the two buses are multiplexed with ports
Memory Space
Von Neumann organization
- linear data/program memory space
64 kbytes
up to 4 Mbytes with memory expansion module
256-byte zero page
58-byte peripheral register space
direct addressable
upper 256-byte interrupt vector table = 128 interrupts
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