Z80 Instruction Set — Control

CALL

CALL imm₁₆

Operation	The current PC value plus three is pushed onto the stack, then is loaded with imm16.
Op Code	11001101 : immLSB : immMSB
T States	17

CALL cc,imm₁₆

Operation	If condition cc is true, the current PC value plus three is pushed onto the stack, then is loaded with imm16.
Op Code	11[cc]100 : immLSB : immMSB Condition Bit Field NZ 000 Z 001 NC 010 C 011 PO 100 PE 101 P 110 M 111
T States	If cc is true: 17 If cc is false: 10

DJNZ

DJNZ imm₈

Operation	The B register is decremented, and if not zero, the signed value imm8 is added to PC. The jump is measured from the address of the instruction op code.
Op Code	00010000 : [imm8]
T States	If B is not 0: 13 If B is 0: 8

JP

JP cc,imm₁₆

Operation	If condition cc is true, imm16 is copied to PC.
Op Code	11[cc]010 : [immLSB] : [immMSB] Condition Bit Field NZ 000 Z 001 NC 010 C 011 PO 100 PE 101 P 110 M 111
T States	10

JR

JR cc,imm₈

Operation	If condition cc is true, the signed value imm8 is added to PC. The jump is measured from the address of the instruction op code.
Op Code	001[cc]000 Condition Bit Field NZ 00 Z 01 NC 10 C 11
T States	If cc is true: 12 If cc is false: 7

NOP

NOP

Operation	No operation is performed.
Op Code	00000000
T States	4

RET

RET

Operation	The top stack entry is popped into PC.
Op Code	11001001
T States	10

RET cc

Operation	If condition cc is true, the top stack entry is popped into PC.
Op Code	11[cc]000 Condition Bit Field NZ 000 Z 001 NC 010 C 011 PO 100 PE 101 P 110 M 111
T States	If cc is true: 11 If cc is false: 5

RETI

RETI

Operation	Used at the end of a maskable interrupt service routine. The top stack entry is popped into PC, and signals an I/O device that the interrupt has finished, allowing nested interrupts (not a consideration on the TI).
Op Code	11101101 : 01001101
T States	14

RETN

RETN

Operation	Used at the end of a non-maskable interrupt service routine (located at $0066) to pop the top stack entry into PC. The value of IFF2 is copied to IFF1 so that maskable interrupts are allowed to continue as before. NMIs are not enabled on the TI.
Op Code	11101101 : 01000101
T States	14

RST

RST imm₈

Operation	The current PC value plus three is pushed onto the stack. The MSB is loaded with $00 and the LSB is loaded with imm8.
Op Code	11[imm8]111 Address Bit Field 00h 000 08h 001 10h 010 18h 011 20h 100 28h 101 30h 110 38h 111
T States	11