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12.1. Instruction Set
The instruction set of the CIP-51 System Controller is fully compatible with the standard MCS-51™ instruc-
tion set; standard 8051 development tools can be used to develop software for the CIP-51. All CIP-51
instructions are the binary and functional equivalent of their MCS-51™ counterparts, including opcodes,
addressing modes and effect on PSW flags. However, instruction timing is different than that of the stan-
dard 8051.
12.1.1. Instruction and CPU Timing
In many 8051 implementations, a distinction is made between machine cycles and clock cycles, with
machine cycles varying from 2 to 12 clock cycles in length. However, the CIP-51 implementation is based
solely on clock cycle timing. All instruction timings are specified in terms of clock cycles.
Due to the pipelined architecture of the CIP-51, most instructions execute in the same number of clock
cycles as there are program bytes in the instruction. Conditional branch instructions take one less clock
cycle to complete when the branch is not taken as opposed to when the branch is taken. Table 12.1 is the
CIP-51 Instruction Set Summary, which includes the mnemonic, number of bytes, and number of clock
cycles for each instruction.
12.1.2. MOVX Instruction and Program Memory
In the CIP-51, the MOVX instruction serves three purposes: accessing on-chip XRAM, accessing off-chip
XRAM, and accessing on-chip program Flash memory. The Flash access feature provides a mechanism
for user software to update program code and use the program memory space for non-volatile data stor-
age (see Section “15. Flash Memory” on page 179). The External Memory Interface provides a fast
access to off-chip XRAM (or memory-mapped peripherals) via the MOVX instruction. Refer to Section
“16. External Data Memory Interface and On-Chip XRAM” on page 187 for details.
Table 12.1. CIP-51 Instruction Set Summary
Mnemonic Description Bytes
Clock
Cycles
Arithmetic Operations
ADD A, Rn Add register to A 1 1
ADD A, direct Add direct byte to A 2 2
ADD A, @Ri Add indirect RAM to A 1 2
ADD A, #data Add immediate to A 2 2
ADDC A, Rn Add register to A with carry 1 1
ADDC A, direct Add direct byte to A with carry 2 2
ADDC A, @Ri Add indirect RAM to A with carry 1 2
ADDC A, #data Add immediate to A with carry 2 2
SUBB A, Rn Subtract register from A with borrow 1 1
SUBB A, direct Subtract direct byte from A with borrow 2 2
SUBB A, @Ri Subtract indirect RAM from A with borrow 1 2
SUBB A, #data Subtract immediate from A with borrow 2 2
INC A Increment A 1 1
INC Rn Increment register 1 1
INC direct Increment direct byte 2 2
INC @Ri Increment indirect RAM 1 2
DEC A Decrement A 1 1
