© 1999 Scenix Semiconductor, Inc. All rights reserved. - 31 - www.scenix.com SX18AC  / SX20AC / SX28AC 15.12.2  Pop Operation
When  a  return  instruction  is  executed  the  subroutine
stack is popped. Specifically, the contents of Stack 1 are
copied into the program counter and the contents of each
stack level are moved to the next higher level. For exam-
ple, Stack 1 receives the contents of Stack 2, etc., until
Stack 7 is overwritten with the contents of Stack 8. Stack
8 is left unchanged, so the contents of Stack 8 are dupli-
cated in Stack 7. 15.13    Comparison and Conditional Branch Instructions The instruction set includes instructions such as DECSZ
fr  (decrement  file  register  and  skip  if  zero),  INCSZ  fr
(increment file register and skip if zero), SNB bit (bit test
file register and skip if bit clear), and SB bit (bit test file
register and skip if bit set). These instructions will cause
the next instruction to be skipped if the tested condition is
true.  If  a  skip  instruction  is  immediately  followed  by  a
PAGE  or  BANK  instruction  (and  the  tested  condition  is
true) then two instructions are skipped and the operation
consumes  three  cycles.  This  is  useful  for  conditional
branching to another page where a PAGE instruction pre-
cedes  a  JMP.  If  several  PAGE  and  BANK  instructions
immediately  follow  a  skip  instruction  then  they  are  all
skipped plus the next instruction and a cycle is consumed
for each. 15.14    Logical Instruction The instruction set contain a full complement of the logi-
cal  instructions  (AND,  OR,  Exclusive  OR),  with  the  W
register  and  a  selected  memory  location  (using  either
direct  or  indirect  addressing)  serving  as  the  two  oper-
ands. 15.15    Shift and Rotate Instructions The  instruction  set  includes  instructions  for  left  or  right
rotate-through-carry. 15.16    Complement and SWAP The device can perform one’s complement operation on
the  file  register  (fr)  and  W  register.  The  MOV  W,<>fr
instruction  performs  nibble-swap  on  the  fr  and  puts  the
value into the W register. 15.17    Key to Abbreviations and Symbols PC<10:0> STACK 1 STACK 2 STACK 3 STACK 4 STACK 5 STACK 6 STACK 7 STACK 8 Symbol Description W Working register fr File register (memory-mapped register in the
range of 00h to FFh) PC                      Lower eight bits of program counter (file regis-
                     ter 02h)
STATUS   STATUS register (file register 03h) FSR File Select Register (file register 04h) C Carry bit in STATUS register (bit 0) DC Digit Carry bit in STATUS register (bit 1) Z Zero bit in STATUS register (bit 2 PD Power Down bit in STATUS register (bit 3) TO                      Watchdog Timeout bit in STATUS register (bit
                     4)
PA2:PA0  Page select bits in STATUS register (bits 7:5) OPTION   OPTION register (not memory-mapped) WDT Watchdog Timer register (not memory-
mapped) MODE MODE register (not memory-mapped) rx Port control register pointer (RA, RB, or RC) ! Non-memory-mapped register designator f File register address bit in opcode k Constant value bit in opcode n Numerical value bit in opcode b Bit position selector bit in opcode . File register / bit selector separator in assem-
bly language instruction # Immediate literal designator in assembly lan-
guage instruction lit Literal value in assembly language instruction addr8 8-bit address in assembly language instruction addr9 9-bit address in assembly language instruction addr12 12-bit address in assembly language instruc-
tion / Logical 1’s complement | Logical OR ^ Logical exclusive OR & Logical AND <> Swap high and low nibbles (4-bit segments) << Rotate left through carry bit >> Rotate right through carry bit - - Decrement file register ++ Increment file register