Measurement Computing Digital488/80A - Manual (Page 35)

Digital488/80A Operation 4
Introduction…… 29
Handshaking/Control Lines…… 29
Clear (Pin 41)…… 30
Data Strobe (Pin 42)…… 30
Trigger (Pin 43)…… 30
Inhibit (Pin 44)…… 31
Service (Pin 45)…… 31
External Data Ready (Pin 46)…… 31
IEEE 488 Bus Support…… 32
Bus Lines…… 32
Bus Commands…… 32
Bus Addresses…… 34
Bus Terminators…… 34
Introduction
Each 40-bit channel has six handshaking/control lines, as follows:
• Clear (Pin 41): This output line is pulsed whenever a Device Clear (
DCL ) or Selected Device Clear
( SDC ) command is received from the IEEE 488 controller.
• Data Strobe (Pin 42): This output is pulsed when the IEEE 488 controller presents new data on the
I/O lines.
• Trigger (Pin 43): This output signal is pulsed when a Group Execute Trigger (
GET ) command is
received on the bus.
• Inhibit (Pin 44): This output line is asserted while the IEEE 488 controller is reading data from input
lines.
• Service (Pin 45): This line is an edge-triggered input that generates a Service Request on the bus.
• External Data Ready (Pin 46): This input line is used to latch digital input data on the I/O lines.
These lines are more-fully discussed in the following text.
Handshaking/Control Lines
The six control lines on each channel enable handshaking of digital I/O data transfer to the Digital488/80A.
They are automatically activated with the corresponding I/O activity and can also be independently
activated with the Handshake (
H ) command. For all descriptions that follow, information on the function
and action of a given line is true for both channels except where noted.
Digital488/80A User’s Manual Digital488/80A Operation 29