ST8 REGISTER SET
The following is a list of the ST8 registers used by ASST8:
a - 8-bit accumulator
xl,yl - LSB of index registers
xh,yh - MSB of index registers
x,y - 16-Bit index registers
sp - 16-bit stack pointer
cc - 8-bit condition code register
ST8 INSTRUCTION SET
The following list specifies the format for each addressing
mode supported by ASST8:
reg register addressing
(a,x,xl,xh,y,yl,yh,sp,cc)
#data immediate data
*saddr 8-bit zero page addressing
0x00 <= saddr <= 0xFF
laddr 16-bit addressing
0x0000 <= laddr <= 0xFFFF
eaddr 24-bit addressing
0x000000 <= eaddr <= 0xFFFFFF
(x) register indirect addressing
(*sofst,r) short indexed (r = x,y,sp)
(sofst,r).b
(lofst,r).w long indexed (r = x,y)
(eofst,r).e extended indexed (r = x,y)
eofst is a lofst value,
i.e. a 16-bit value where
(eofst,r).e points to a
24-bit address
(ofst,r) for the ldf instruction the
(eofst,r).e mode is selected
else
(ofst,r) if ofst is relocatable or
an external value then
the (lofst,r).w mode is
selected by default
else
(ofst,r) if ofst is a locally
defined constant then
the (sofst,r).b mode
is selected when
0x00 <= ofst <= 0xFF else
the (lofst,r).w mode
is selected
Instructions supporting
only a single form will
use the appropriate form
but will report an error.
[*saddr] short indirect
[saddr].b
[laddr].w long indexed
[eaddr].e extended indexed
[addr] for the callf, jpf, and ldf
instructions the [eaddr].e
mode is selected
else
[addr] if addr is relocatable or
an external value then
the [laddr].w mode is
selected by default
else
[addr] if addr is a locally
defined constant then
the [saddr].b mode
is selected when
0x00 <= addr <= 0xFF else
the [laddr].w mode
is selected
Instructions supporting
only a single form will
use the appropriate form
but will report an error.
([*saddr],r) short indirect indexed
([saddr].b,r) (r = x,y)
([saddr],r).b
([laddr].w,r) long indirect indexed
([laddr],r).w (r = x,y)
([eaddr].e,r) extended indirect indexed
([eaddr],r).e (r = x,y)
([addr],r) for the ldf instruction the
([eaddr],r).e mode is selected
else
([addr],r) if addr is relocatable or
an external value then
the ([laddr],r).w mode is
selected by default
else
([addr],r) if addr is a locally
defined constant then
the ([saddr],r).b mode
is selected when
0x00 <= addr <= 0xFF else
the ([laddr],r).w mode
is selected
Instructions supporting
only a single form will
use the appropriate form
but will report an error.
label pc-relative branch addressing
The terms data, saddr, laddr, eaddr, addr, sofst, lofst, eofst,
ofst, and label may all be expressions.
Note that not all addressing modes are valid with every in-
struction, refer to the ST8 technical data for valid modes.
The following tables list all ST8 mnemonics recognized by the
ASST8 assembler. The designation [] refers to a required ad-
dressing mode argument.
Inherent Instructions
nop trap
wfi wfi
halt ret
retf iret
sim rim
scf rcf
rvf ccf
Conditional Branch Instructions
jra label
jrt label jrf label
jrugt label jrule label
jruge label jrult label
jrnc label jrc label
jrne label jreq label
jrnv label jrv label
jrpl label jrmi label
jrsgt label jrsle label
jrsge label jrslt label
jrnh label jrh label
jrnm label jrm label
jril label jrih label
Bit Test and Branch Instructions
btjt laddr,#,label
btjf laddr,#,label
Bit Manipulation Instructions
bccm laddr,#
bcpl laddr,#
bset laddr,#
bres laddr,#
Single Operand Instructions
neg [] cpl []
srl [] rrc []
sra [] rlc []
sll [] sla []
dec [] inc []
tnz [] swap []
clr []
negw reg cplw reg
srlw reg rrcw reg
sraw reg rlcw reg
sllw reg slaw reg
decw reg incw reg
tnzw reg swapw reg
clrw reg
pop reg push reg
Double Operand Instructions
add a,[] adc a,[]
and a,[] bcp a,[]
cp a,[] or a,[]
sbc a,[] sub a,[]
xor a,[]
add sp,# sub sp,#
addw reg,[] subw reg,[]
cpw reg,[]
mul x,a mul y,a
div x,a div y,a
divw x,y
exg a,reg exg a,laddr
exgw x,y
rrwa x,a rrwa y,a
rlwa x,a rlwa y,a
ld [],[]
ldf a,[] ldf [],a
ldw reg,[] ldw [],reg
mov saddr,saddr
mov laddr,laddr mov laddr,#
Call to Subroutine and Jump Instructions
call [] jp []
callf eaddr callf [eaddr].e
jpf eaddr jpf [eaddr].e
callr label
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Last Updated: September 2023