Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 176)

Section 7 Peripheral Pass-Thru Operation
7.4
When serial data is received, DIO5 of the Serial Poll byte is set, '1', to
indicate to the IEEE controller that the serial input buffer is NOT EMPTY. If
set, it indicates that at least one character is available in the serial input
buffer to be read by the IEEE controller. Once all of the serial input data is
read by the IEEE controller this bit is reset.
The Micro488/EX can generate a request for service on the bus when
it receives the last serial terminator. To enable this feature, the Pass-Thru
Feature switch, located on the internal switch bank of SW1, must be set to
open. When enabled, the Micro488/EX will assert the IEEE bus SRQ line
and set serial poll status bits DIO7 and DIO3 when the last serial
terminator is detected. The IEEE controller must perform a serial poll on
the interface to clear the SRQ. If the Pass-Thru Feature switch is in the
closed position, there will not be any indication in the serial poll status byte
that a serial terminator has been received.
SW1 View For Selecting SRQ on Last Terminator
OPEN
1 2 3 4 5 6 7 8 DOT
Switch
Side
View
OPEN
1 2 3 4 5 6 7 8
SRQ on Last
Terminator Disabled
SRQ on Last
Terminator Enabled
7.4 Serial Poll Status Byte Register
The following shows and describes the serial poll status information provided by
the Micro488/EX.
DIO8 IEEE Input Buffer NOT EMPTY
This bit is set when the IEEE input buffer contains one or more
data bytes which have not been sent out the serial port. It is
cleared, set to "0", when the buffer is empty.