~ National ~ Semiconductor - Al Kossow's Bitsavers

6.0 Instruction Set Reference (Continued)
SBCA Subtract with Carry and Accumulator
Syntax
SBCA Rs, Rd
SBCA Rs, [mlr]
Affected Flags
N,Z,C,V
Description
-register, register
-register, indexed
Subtracts the active accumulator and the carry flag from the
source register Rs, placing the result into the destination
specified. The destination may be either a register, Rd, or
data memory via an index register mode, [mlr]. Negative
results are represented using the two's complement format.
Note that register bank selection determines which accumulator
is active.
Example
Subtract the constant 109 from the index register IW, (which
is 16 bits wide).
SUBA A, A ;Clear the accumulator
SUB 109, R12 ;Iow byte of IW-109
SBCA R13, R13 ;high byte of IW-borrow
Instruction Format
SBCA Rs, Rd
15 9
SBCA
Rs, [mlr]
1
Rd
1 11011101011111 1 1 1
_ Opcode . m • Ir .
15 8 6 4
T-states
SBCA
SBCA
Rs, Rd
Rs, [mlr]
Bus Timing
SBCA Rs, Rd
SBCA Rs, [mlr]
00 - post-decrement
01 - no change
10 - post Increment
11 - pre-Increment
-2
-3
-Figure 7
-Figure 12
4
Rs
Rs
t
00 - IW
01 - IX
10 - IY
11 - IZ
Operation
SBCA Rs, Rd
Rs - accumulator - carry bit ~ Rd
SBCA Rs, [mlr]
Rs - accumulator - carry bit ~ data memory
o
o
TL/F9336-13
SHL
Syntax
SHL
Shift Left
Rsd, b
Affected Flags
N,Z,C
-register
Description
Shifts the contents of the register Rsd b bits to the left and
places the result back into that register. Zeros are shifted in
from the right, (i.e., from the LSB). The value b may specify
from 0 to 7 bit shifts. The Carry flag contains the last bit
shifted out.
Example
Place a new internal Address Stack Pointer into the Internal
Stack Pointer register (iSP l. R30. Assume that the new
[ASP] is located in register 20.
MOVE ISP,RB ;read (iSP) for [DSP]
AND 00001111 B,RB ;save [DSP] only
SHL R20,4 ;Ieft justify [ASP]
ORA R20,ISP ;combine [ASP] + [DSPl.
; then place into (iSP)
Instruction Format
11111010111010111
Opcode
15
T-states
2
Bus Timing
Figure 7
Operation
7
1 1
(B-b)
Rsd
4 o
TL/F/9336-14
2-120