SAP-Plus Instructions
SAP-Plus Instructions
The SAP-Plus has a single user-accessable register A that functions as the accumulator for ALU operations. If no stack operations are needed, then the SP can also be used as a general purpose register.
The memory features two 256 byte areas that are addressed by the Memory Address Register. The Program Memory area stores the instructions and instruction arguments. The data area is used for the stack and for data storage with the Load, Store, and arithmetic operations.
The stack pointer must be initialized before the stack is used. This can be done using LAI to load a value into A and TAS to move it to the SP. Because the stack grows downward, it is recomended that the SP be initialized to the value 255 so it can use the top section of the data memory. General data storage can then start at zero and grow upward.
| ACI | ACM | ADI | ADM | ASL | CLF | CPI | CPM |
| CYN | DCA | DCS | INA | INS | JC | JEQ | JGE |
| JLT | JMP | JNC | JNE | JNZ | JSR | JZ | LAI |
| LAM | LAX | NOP | NOT | OUT | PHA | PLA | RC |
| REQ | RGE | RLT | RNC | RNE | RNZ | RTS | RZ |
| SAM | SAX | SBI | SBM | SCI | SCM | SEF | TAS |
| TSA | TST |
ACI
add immediate to A with carry
Add A to immediate value and store the result in A. The Carry flag value is included in the addition. If Carry is set, the value in A will be A+value+1.
Carry Flag: set if A overflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| ACI | 0x24 | 2 | 5 |
ACM
add memory to A with carry
Add A to value in data memory at the address argument and store the result in A. The Carry flag value is included in the addition. If Carry is set, the value in A will be A+value+1.
Carry Flag: set if A overflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| ACM | 0x25 | 2 | 6 |
ADI
add immediate to A
Add A to immediate value and store the result in A. The Carry flag value is not used in the addition.
Carry Flag: set if A overflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| ADI | 0x20 | 2 | 5 |
ADM
add memory to A
Add A to value in data memory at the address argument and store the result in A. The Carry flag value is not used in the addition.
Carry Flag: set if A overflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| ADM | 0x21 | 2 | 6 |
ASL
arithmetic shift left A
Shift A one position left. Least significant bit of A takes the value of the Carry flag and the Carry Flag is set with the most significant bit of A.
Carry Flag: set if A overflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| ASL | 0x0a | 1 | 4 |
CLF
clear carry and zero flags
Clear carry and zero flags.
Carry Flag: clear
Zero Flag: clear
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| CLF | 0x0c | 1 | 4 |
CPI
compare immediate to A
Compare A to immediate value in the next byte of program memory. Carry flag is clear if A<value and Zero flag is set if A=value. The value of A is not changed.
Carry Flag: clear if A < value
Zero Flag: set if equal
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| CPI | 0x28 | 2 | 5 |
CPM
compare memory to A
Compare A to the value in data memory addressed by the next byte of program memory. Carry flag is clear if A<value and Zero flag is set if A=value. The value of A is not changed.
Carry Flag: clear if A < value
Zero Flag: set if equal
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| CPM | 0x29 | 2 | 6 |
CYN
can you not
Toggles A between its original value and NOT A. The value is swapped seven times, so the final value is NOT A at the end of the instruction. Because A toggles between two values, this can be used to create a noticable visual indicator for a spin loop when a program completes. Useful starting values for A are 0x55, 0xf0, or 0xcc.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| CYN | 0x3f | 1 | 16 |
DCA
decrement A
Decrement A.
Carry Flag: clear if wrap past zero
Zero Flag: set if A decremented to zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| DCA | 0x08 | 1 | 4 |
DCS
decrement SP
Decrement the Stack Pointer. Not needed for normal stack operation. Manipulates SP when SP is used as an index register.
Carry Flag: undetermined
Zero Flag: set is SP is sero after decrement
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| DCS | 0x1e | 1 | 4 |
INA
increment A
Increment A.
Carry Flag: set if wrap to zero
Zero Flag: set if wrap to zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| INA | 0x07 | 1 | 4 |
INS
increment SP
Increment the Stack Pointer. Not needed for normal stack operation. Manipulates SP when SP is used as an index register.
Carry Flag: undetermined
Zero Flag: set is SP is sero after increment
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| INS | 0x1d | 1 | 4 |
JC
jump on Carry
Jump to address argument if Carry flag set
Alias: JGE - jump if greater or equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JC | 0x11 | 2 | 4 |
JMP
jump unconditional
Jump to address argument
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JMP | 0x10 | 2 | 4 |
JNC
jump on no Carry
Jump to address argument if Carry flag clear
Alias: JLT - jump if less than
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JNC | 0x13 | 2 | 4 |
JNZ
jump on no Zero
Jump to address argument if Zero flag clear
Alias: JNE - jump if not equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JNZ | 0x14 | 2 | 4 |
JSR
jump to subroutine
Jump to subroutine at address argument. PC is stored on the stack and then SP is decremented.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JSR | 0x17 | 2 | 7 |
JZ
jump on Zero
Jump to address argument if Zero flag set
Alias: JEQ - jump if equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| JZ | 0x12 | 2 | 4 |
LAI
load A immediate
Load A with immediate value stored in the next byte in program memory.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| LAI | 0x02 | 2 | 4 |
LAM
load A from memory
Load A with the value from memory address specified by the next byte in program memory.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| LAM | 0x03 | 2 | 5 |
LAX
load A indexed by SP
Load A from memory indexed by SP. This is similar to a PLA operation except the value of SP is not changed.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| LAX | 0x0e | 1 | 4 |
NOP
no operation
No operation is performed. Data registers and flags are unchanged.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| NOP | 0x00 | 1 | 3 |
NOT
NOT A
Replace A with the logical NOT of A, meaning that all zero bits become one and all one bits become zero.
Carry Flag: undetermined
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| NOT | 0x09 | 1 | 4 |
OUT
output A
Store A in the Output Register for display.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| OUT | 0x01 | 1 | 3 |
PHA
push A
Push accumulator onto to the stack. The value of A is first written to the RAM location pointed to by SP and then SP is decremented.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| PHA | 0x15 | 1 | 5 |
PLA
pull A
Pull accumulator from the stack. SP is incremented and then the value for A is read from RAM at the new SP location.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| PLA | 0x16 | 1 | 5 |
RC
return if carry
Return from subroutine if Carry flag is set else no operation.
Alias: RGE - return if greater or equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| RC | 0x19 | 1 | 5 |
RNC
return if not carry
Return from subroutine if Carry flag is not set else no operation.
Alias: RLT - return if less than
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| RNC | 0x1b | 1 | 5 |
RNZ
return if not zero
Return from subroutine if Zero flag is not set else no operation.
Alias: RNE - return if not equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| RNZ | 0x1c | 1 | 5 |
RTS
return from subroutine
Return from subroutine. SP is incremented and then PC is read from RAM at the new SP location.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| RTS | 0x18 | 1 | 5 |
RZ
return if zero
Return from subroutine if Zero flag is set else no operation.
Alias: REQ - return if equal
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| RZ | 0x1a | 1 | 5 |
SAM
store A to memory
Store A to memory at the address specified by the next byte in program memory.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SAM | 0x04 | 2 | 5 |
SAX
store A indexed by SP
Store A to memory indexed by SP. This is similar to a PHA operation except the value of SP is not changed.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SAX | 0x0f | 1 | 4 |
SBI
subtract immediate from A
Subtract immediate value from A and store the result in A. The Carry flag value is not used in the addition.
Carry Flag: clear if A underflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SBI | 0x22 | 2 | 5 |
SBM
subtract memory from A
Subtract value in data memory at the address argument from A and store the result in A. The Carry flag value is not used in the compuation.
Carry Flag: clear if A underflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SBM | 0x23 | 2 | 6 |
SCI
subtract immediate from A with carry
Subtract immediate value from A and store the result in A. The Carry flag is included in the subtraction. If Carry is clear, the value in A will be A-value-1.
Carry Flag: clear if A underflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SCI | 0x26 | 2 | 5 |
SCM
subtract memory from A with carry
Subtract value in data memory at the address argument from A and store the result in A. The Carry flag is included in the subtraction. If Carry is clear, the value in A will be A-value-1.
Carry Flag: clear if A underflows
Zero Flag: set if zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SCM | 0x27 | 2 | 6 |
SEF
set carry and zero flags
Set carry and zero flags.
Carry Flag: set
Zero Flag: set
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| SEF | 0x0d | 1 | 4 |
TAS
transfer A to SP
Transfer A to the SP register. A is unchanged.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| TAS | 0x05 | 1 | 3 |
TSA
transfer SP to A
Transfer the value of the SP register to A. SP is unchanged.
Carry Flag: unchanged
Zero Flag: unchanged
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| TSA | 0x06 | 1 | 3 |
TST
test A
Test A for sign and zero. Carry flag becomes a minus flag (A<0). The Zero flag is set if A=0.
Carry Flag: set if A is negative
Zero Flag: set if A is zero
| Name | Opcode | Bytes | Cycles |
|---|---|---|---|
| TST | 0x0b | 1 | 4 |
this file was generated by sap-plus-instructions.py at 01-Feb-2025 12:32:01