Zilog ZUSBOPTS - Manual (Page 253)

UM017105-0511 Expressions
Zilog Developer Studio II – ZNEO™
User Manual
225
XREF erw1:EROM ; erw1 declared to be in EROM
Register Lists for PUSHM and POPM Instructions
The ZNEO processor provides the PUSHM and POPM instructions to push or pop multiple
registers. (Actually, the ZNEO processor provides the PUSHMHI , PUSHMLO , POPMHI , and
POPMLO instructions, which each push or pop half the register set.The ZNEO assembler
accepts PUSHM and POPM and generates the lower level instructions.) The list of registers
to be pushed or popped can be expressed either as a register list or as an immediate value.
If an immediate value is used, the least significant bit represents R0, and the most signifi-
cant bit represents R15. The following examples illustrate the syntax for register lists:
myFunction:
PUSHM ; Save registers R0,R1,R2,R8, and R12
; Code for myFunction
POPM ; Restore Registers
RET ; and return
; The same example, using immediate values:
hisFunction:
PUSHM #1107H ; Save registers R0,R1,R2,R8, and R12
; Code for hisFunction
POPM #1107H ; Restore Registers
RET ; and return
; The same example, using equates:
RegList EQU " "
herFunction:
PUSHM RegList ; Save registers
; Code for herFunction
POPM RegList ; Restore Registers
RET ; and return
Instruction Alignment
Because all ZNEO instructions must be aligned to an even address, the ZNEO assembler
implicitly inserts an ALIGN directive in front of each instruction. Thus, the following
example assembles correctly:
; Some code
RET
_L1: DW %1234 ; Some data, perhaps used by previous routine
DB %3 ; Warning, next address is odd
myFunction: ; OK, implicitly aligned to next even address
LINK #%20
Of course, it does no harm to insert an ALIGN 2 or a .EVEN directive ahead of a function,
just to be safe.