Measurement Computing Digital488/80A - Manual (Page 38)

IEEE 488 Bus Support
The Digital488/80A implements many of the capabilities defined by the IEEE 488 1978 specification.
These capabilities are discussed in the following text. However, the bus lines (uniline) and bus commands
(multiline) that the Digital488/80A does not support, or respond to, include the following:
REN Remote Enable (uniline) PPC Parallel Poll Configure
GTL Go to Local PPD Parallel Poll Disable
LLO Local Lock Out PPU Parallel Poll Unconfigure
PP Parallel Poll TCT Take Control
Bus Lines
The following IEEE 488 bus management lines are supported by Digital488/80A:
• Interface Clear (
IFC ): IFC places the Digital488/80A in the Talker/Listener Idle State, and pulses the
Clear output line for approximately 50 microseconds.
• Service Request (
SRQ ): Whenever the Digital488/80A generates a Service Request ( SRQ ), a Serial
Poll of either channel will return a Serial Poll Status byte of at least 64 (decimal) showing that the SRQ
was generated by the Digital488/80A.
In order to determine which channel generated the SRQ , use the Service Request Mask ( M ) command
with the Query ( ? ) option, or M? , to recall what SRQ conditions are selected. The Digital488/80A
returns M0 if SRQ s are disabled, or returns a response between either M1 through M7 , or M16 through
M23 , depending on what SRQ s conditions are selected.
The following BASIC program illustrates one approach for handling Service Requests:
PRINT#1,"SPOLL08"
INPUT#2,SRQ08 Serial poll Channel 0
PRINT#1,"SPOLL09"
INPUT#2,SRQ09 Serial poll Channel 1
PRINT#1,"OUTPUT08;M?"
PRINT#1,"ENTER08"
INPUT#2,M08$ Retrieve SRQ selection(s) from Channel 0
PRINT#1,"OUTPUT09;M?"
PRINT#1,"ENTER09"
INPUT#2,M09$ Retrieve SRQ selection(s) from Channel 1
IF M08$="M0" THEN GOTO 500 SRQs disabled Channel 0, test Channel 1
IF M08$="M1" AND SRQ08 = 65 THEN GOTO 600 Service input transition routine, Channel 0
IF M08$="M2" AND SRQ08 = 66 THEN GOTO 700
EDR EDR input transition routine, Channel 0
IF M08$="M4" AND SRQ08 = 70 THEN GOTO 800 Bus error routine, Channel 0
Note: To allow the Digital488/80A to detect each of the above conditions, the Service Request
Mask (
M ) command must be executed for each condition. More extensive comparisons of the
Serial Poll Status Byte and the M? response are needed if multiple SRQ conditions are
selected. Refer to the Service Request Mask ( M ) command in Chapter 6: Digital488/80A
Commands.
The Digital488/80A unit may be programmed to generate an SRQ on power-up by selecting the SRQ on
Ready option ( M16 ) of the Service Request Mask ( M ) command, and saving this selection as part of the
power-up configuration (Configuration 0).
Bus Commands
The following IEEE 488 bus commands are supported by Digital488/80A:
32 Digital488/80A Operation Digital488/80A User's Manual