Xerox 560 Reference Manual page 93

Instruction Name
Mnemonic
Translate Byte String TBS
Trans
I
ate and Test Byte Stri ng
TTBS
Edit Byte String
EBS
These instructions are in the immediate byte operand class
and are memory-to-memory operations. These operations
are under the control of information that must be loaded
into certain general registers before the instruction is exe-
cuted. Except for the MOVE BYTE STRING instruction,
which proceeds four bytes at a time under certain condi-
tions, a byte string instruction proceeds one byte at a time
and may be interrupted after any individual byte operation.
Upon return, execution resumes from the pointofinterruption.
The general format for the information in the instruction
word and in the general registers is as follows:
Instruction word:
Contents of register R:
Contents of register Ru 1 :
Count
Desi gnation
Operation
R
Displacement
Mask/Fill
Source Address
Desti nation
nrlrlr~~~
Function
The 7-bit operation code of the instruc-
tion. (If any byte-string instruction is
indirectly addressed, the basi c processor
traps to location X l 40
1
at the time of op-
eration code decoding. )
The 4-bit field that identifies register R
of the current general register block.
A 20-bit field that contains a signed
byte displacement va lue, used to form
an effective byte address. The displace-
ment value is right-justified in the 20-bit
field, and negative values are in twols
complement form.
An 8-bit field used only with TRANSLATE
AND TEST BYTE STRING and EDIT BYTE
STRING. The purpose of this field is
explained in the detai led discussion of
the TTBS and EBS instructions.
A 19-bit field that normally contains the
byte address of the first (most significant)
Designation
Source Address
(cont. )
Count
Destination
Address
Function
byte of the source byte string operand.
The effective source address is the source
address in register R plus the displacement
value in the instruction word.
An 8-bit field that contains the true count
(from 0 to 255) of the number of bytes
involved in the operation. This field is
decremented by 1 as each byte in the
destination byte string is processed. A
o
count means IIno operation ll with re-
spect to the registers and main memory.
A 19-bit field that contains the byte
address of the first (most significant)
byte of the destination byte-string oper-
and. This field is incremented by 1 as
each byte in the destination byte string
is processed.
In any byte-string instruction, any portion of register R
or Ru1 that is not explicitly defined
(i.
e., bit posi-
tions 8-12), should be coded with zeros for real and virtual
addressi ng.
Since the value Ru1 is obtained by performing a logical
inclusive OR with the value 0001 and the value of the
R field of the instruction word, the two control registers
are Rand R
+
1
if
R is even. However, if R is an odd value,
register R contains an address value that functions both as a
source operand address and as a destination operand address.
Also,
if
register 0 is designated in any byte-string instruc-
... ___ 1 _______ ..
~
___
TnA ... IC"1 ATe A"'I/""'\ TeC"T n'\rre C"TnT"'I"" ____ I
IIVII \CAvCPI IVI "'\r\I'4"'LJ"'IL r\1'4V IL ... I U , I ........ '\11'4'\,.7 UIIU
EDIT BYTE STRING), its contents are ignored and a zero
source address value is obtained. Thus, the following
three cases exist for most byte-string instructions, depending
on whether the value of the R field of the instruction word
is even and nonzero, odd, or zero:
Case I, R is even and nonzero
The effective source address is the address in register R plus
the displacement in the instruction word; the destination
address is the address in register R + 1, but without the
displacement added.
Case II, R is odd
The effective source address is the address in register R plus
the displacement in the instruction word; the destination
address is also the address in register R, but without the
displacement added.
Case III, R is zero
The effective source address is the displacement value in
the instruction word; the destination address is the address
in register 1. In this case, the source byte-string operand
is always a single byte.
Byte-String Instructions 87