Return from Subroutine
RET pops the high- and low-order bytes of the PC successively from the stack, decrementing the Stack Pointer by two. Program execution continues at the resulting address, generally the instruction immediately following an ACALL or LCALL. No flags are affected.
Encoding: 0 0 1 0 0 0 1 0
The Stack Pointer originally contains the value 0BH. Internal RAM locations 0AH and 0BH contain the values 23H and 01H, respectively. The following instruction,
RET
leaves the Stack Pointer equal to the value 09H. Program execution continues at location 0123H.
Return from Interrupt
RETI pops the high- and low-order bytes of the PC successively from the stack and restores the interrupt logic to accept additional interrupts at the same priority level as the one just processed. The Stack Pointer is left decremented by two. No other registers are affected; the PSW is not automatically restored to its pre-interrupt status. Program execution continues at the resulting address, which is generally the instruction immediately after the point at which the interrupt request was detected. If a lower- or same-level interrupt was pending when the RETI instruction is executed, that one instruction is executed before the pending interrupt is processed.
Encoding: 0 0 1 1 0 0 1 0
The Stack Pointer originally contains the value 0BH. An interrupt was detected during the instruction ending at location 0122H. Internal RAM locations 0AH and 0BH contain the values 23H and 01H, respectively. The following instruction,
RETI
leaves the Stack Pointer equal to 09H and returns program execution to location 0123H.
Difference between the RET and RETI instructions
Both perform the same actions of popping off the top two bytes of the stack into the program counter, and making the 8051 return to where it left off. However, RETI also performs an additional task of clearing the interrupt-in-service flag, indicating that the servicing of the interrupt is over and the 8051 now can accept a new interrupt on that pin. If you use RET instead of RETI as the last instruction of the interrupt service routine, you simply block any new interrupt on that pin after the first interrupt, since the pin status would indicate that the interrupt is still being serviced. In the cases of TFO, TF1, TCON.l, and TCON.3, they are cleared by the execution of RETI.
RET pops the high- and low-order bytes of the PC successively from the stack, decrementing the Stack Pointer by two. Program execution continues at the resulting address, generally the instruction immediately following an ACALL or LCALL. No flags are affected.
Encoding: 0 0 1 0 0 0 1 0
The Stack Pointer originally contains the value 0BH. Internal RAM locations 0AH and 0BH contain the values 23H and 01H, respectively. The following instruction,
RET
leaves the Stack Pointer equal to the value 09H. Program execution continues at location 0123H.
Return from Interrupt
RETI pops the high- and low-order bytes of the PC successively from the stack and restores the interrupt logic to accept additional interrupts at the same priority level as the one just processed. The Stack Pointer is left decremented by two. No other registers are affected; the PSW is not automatically restored to its pre-interrupt status. Program execution continues at the resulting address, which is generally the instruction immediately after the point at which the interrupt request was detected. If a lower- or same-level interrupt was pending when the RETI instruction is executed, that one instruction is executed before the pending interrupt is processed.
Encoding: 0 0 1 1 0 0 1 0
The Stack Pointer originally contains the value 0BH. An interrupt was detected during the instruction ending at location 0122H. Internal RAM locations 0AH and 0BH contain the values 23H and 01H, respectively. The following instruction,
RETI
leaves the Stack Pointer equal to 09H and returns program execution to location 0123H.
Difference between the RET and RETI instructions
Both perform the same actions of popping off the top two bytes of the stack into the program counter, and making the 8051 return to where it left off. However, RETI also performs an additional task of clearing the interrupt-in-service flag, indicating that the servicing of the interrupt is over and the 8051 now can accept a new interrupt on that pin. If you use RET instead of RETI as the last instruction of the interrupt service routine, you simply block any new interrupt on that pin after the first interrupt, since the pin status would indicate that the interrupt is still being serviced. In the cases of TFO, TF1, TCON.l, and TCON.3, they are cleared by the execution of RETI.
Related topics:
8051 Long Call | 8051 Absolute Call | 8051 Long Jump | 8051 Absolute Jump | 8051 Short Jump | 8051 Indirect Jump
List of topics: 8051
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