Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 136)

Section 5 Command Descriptions
5.66
REQUEST
In Peripheral mode, the Micro488/EX is able to request service from the Active
Controller by asserting the Service Request bus signal. The REQUEST command sets
the Serial Poll status (including Service Request) of the Micro488/EX. REQUEST
takes a numeric argument in the range of 0 to 255 (&H0 to &HFF) that is used to set
the Serial Poll status. When the Micro488/EX is Serial Polled by the Controller, it
returns this byte on the DIO data lines.
The data lines are numbered DIO8 through DIO1. DIO8 is the most significant
line and corresponds to a value of 128 (&H80). DIO7 is the next most significant line
and corresponds to a value of 64 (&H40). DIO7 has a special meaning: It is the
Request For Service (rsv) bit. REQUEST always forces this bit to a '1' which generates
a service request (SRQ) to the controller.
When the Micro488/EX is Serial Polled, all eight bits of the Serial Poll status are
returned to the Controller. The rsv bit is cleared when the Micro488/EX is Serial
Polled by the Controller. This causes the Micro488/EX to stop asserting SRQ. The
Micro488/EX will also un-assert rsv when it receives a Device Clear (DCL) or Selected
Device Clear (SDC) from the active controller.
SYNTAX REQUEST[;][status]
or
REQ[;][status]
status is the service request status in the range of 0 to 255. If
status is not specified, only rsv (DIO7) is asserted.
RESPONSE None
MODE *CA
BUS STATES SRQ
EXAMPLES PRINT#1,"REQUEST";2+4
Generate an SRQ (64) with DIO2 (2) and DIO3 (4)
set in the Serial Poll Response.
PRINT#1,"REQUEST" Generate an SRQ (64)