Measurement Computing Serial488A - Manual (Page 53)

4.4
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 Serial488A can generate a request for service on the bus when it
receives the last serial terminator. To enable this feature, the Peripheral
SRQ switch, located on the internal switch bank of SW1, must be enabled.
When enabled, the Serial488A 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 Peripheral SRQ switch is in the disabled position,
there will still be an indication in the serial poll status byte that the last
serial input terminator was received, but Serial488A will not generate a
service request (SRQ).
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
4.4 Serial Poll Status Byte Register
The following shows and describes the serial poll status information provided by
the Serial488A.
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.