Xerox 560

CAll INSTRUCTIONS
Each ofthe four CA LL instructions causes the basi c processor
to trap to a specifi c location for the next instruction in se-
quence. The four CALL instructions, their mnemonics, and
the locations to wh i ch the basi c processor traps are:
Instru ct ion
Trap
Name
Mnemonic
Location
CALL 1
CAll
X'48'
CALL 2
CAL2
X'49'
CALL 3
CAL3
X'4A'
CALL 4
CAL4
X'4B'
Each ofthese four trap locations must contain an EXCHANGE
PROG RAM STATUS WORDS (XPSD) instruction. Execution
of XPSD in the trap location for a CALL instruction is de-
scribed under "Control Instructions, XPSD Exchange Pro-
gram Status Words". If the XPSD instruction is coded with
bit position 9 set to 1, the next instruction (executed after
the XPSD) is taken from one of 16 possible locations, as
designated by the value in the R field of the CALL instruc-
tion. Each of the 16 locations may contqin an instruction
that causes the basic processor to branch to a specific
routine; thus, the four CALL instructions can be used to
enter any of as many as 64 unique routines.
The effective address of either a direct or indirect CALL
instruction is not used for a memory reference and, there-
fore, cannot cause a trap.
CALI CALL 1
(Word index alignment)
CALL 1 causes the basi c processor to trap to location X'48'.
CAL2 CALL 2
(Word
index alignment)
CAL4
CALL 4
(Word
index al ignment)
~
CALL 4 causes the basic processor to trap to location X'4B'.
CONTROL INSTRUCTIONS
The following privileged instructions are used to control the
basi c operating conditions-of the basic processor:
Instruction Name
Mnemonic
Load Program Status Words
LPSD
Exchange Program Status Words
XPSD
Load Register Pointer
LRP
Move to Memory Contro I
MMC
Load
Real Address
LRA
Load Memory Status
LMS
Wait
WAIT
Read
Direct
RD
Write Direct
WD
If execution of any control instruction is attempted while
the basic processor is in the slave mode (i. e., while bit 8
of the current program status words is a 1), the basi c pro-
cessor unconditionally traps to location X'40' prior to
executing the instruction.
PROGRAM STATUS WORDS
Program status words have the following structure when
stored in memory:
CA
LL 2 causes the basi c processor to trap to location X '49'. Bit
CAL3
CALL 3
(Word
index al ignment)
CA
LL 3 causes the basi c processor to trap to location X '4A '.
Position
0-3
4
5
6
7
Designation
CC
FR
FS
FZ
FN
Function
Condition code
Floating round
Floating significance mask
Floating zero mask
Floating normal ize mask
Call Instructions/Control Instructions 109