Tektronix 2714, Programmer'S Manual

Page: 287 / 308

Appendix B: GPIB System Concepts
2714 & 2715 Programmer Manual
B–11
0
1
0
1
1
1
1
1
0
0
1
1
1
1
1
1
0
1
0
0
0
0
1
0
0
1
0
0
0
0
0
1
0
1
1
0
1
1
0
0
0
0
1
0
1
1
0
0
DATA
BUS
DIO8
DIO1
ATN Asserted EOI Asserted ATN Asserted
UNT UNL “B” “A”
Secondary
Address
Primary
Address
Instruments
95 63 65 108 44 66
Controller
Figure B–3: Example of Data Byte Traffic
To complete the sequence, the controller activates the ATN line again and sends
the universal Unlisten (UNL) and Untalk (UNT) commands to clear the bus. Six
handshake cycles on the data transfer control bus are required to send the six data
bytes.
Each time a data byte is transferred over the data bus, an enabled talker and all
enabled listeners execute a handshake sequence via signal lines DAV, NRFD, and
NDAC (see Figure B–4 — the ATN line is shown to illustrate the controller’s
role in the process).
Transfer Bus (Handshake)