Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 177)

Section 7 Peripheral Pass-Thru Operation
7.5
Serial Poll Status Byte
DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1
1 4 2 8 16 32 64 128
IEEE Input Bu
ffer Not Empt
y
Not Used - Al
ways '0'
Serial Handsh
ake
Not Used - Al
ways '0'
Serial Input
Buffer Not Em
pty
Request Servi
ce - rsv bit
IEEE Input Bu
ffer Full
Last Serial I
nput Terminat
or
DIO7 rsv
This bit is defined by the IEEE 488 Specification and is used to
indicate to the bus controller that the Micro488/EX is the bus
device that requested service. It is cleared when the interface is
serial polled by the controller.
DIO6 Not Defined - Always "0"
DIO5 Serial Input Buffer NOT EMPTY
This bit is set when the serial input buffer contains one or more
data bytes which have not been sent out the IEEE bus. It is
cleared, set to "0", when the buffer is empty.