There was no unconditional jump instruction, nor was there a procedure call instruction-it had not yet been invented.
12.
Special jump and call instructions ( AJMP and ACALL ) make access within the same 2 KiB of program memory slightly smaller.
13.
An exception is encountered when the execution unit encounters a branch instruction i . e . either a jump or a call instruction.
14.
In a similar manner, subroutine call instructions can be indirect, with the address of the subroutine to be called specified in memory.
15.
The prologue will commonly save the return address left in a register by the call instruction by pushing the value onto the call stack.
16.
Most access to supervisor services is via system subroutines that issue the necessary Supervisor Call instructions ( SVCs ) rather than by direct use of SVCs.
17.
Note that a CALL instruction only includes 8 bits of address, and may only specify addresses in the first half of each 512-word page.
18.
Some subsystems, usually consisting of pure code, such as the run time libraries, may be the direct target of a Call instruction without requiring a gate.
19.
The interrupt cycle of the 8080 / 8085 will issue three bytes on the data bus ( corresponding to a CALL instruction in the 8080 / 8085 instruction set ).
20.
Alternatively, some instruction set architectures automatically provide comparable functionality as part of the action of the call instruction itself, and in such an environment the prologue need not do this.
