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RS-232↔IEEE 488 INTERFACE CONVERTER
Figure 6-2. IEEE Bus Handshaking.
6.6 Data Lines
The GPIB provides eight data lines for a bit-parallel/byte-serial data transfer.
These eight data lines use the convention of DIO1 through DIO8 instead of
the binary designation of D0 to D7. The data lines are bidirectional and are
active low.
6.7 Multiline Commands
Multiline (bus) commands are sent by the Active Controller over the data bus
with ATN asserted. These commands include addressing commands for talk,
listen, Untalk, and Unlisten.
6.7.1 G
O
T
O
L
OCAL
(GTL)
This command allows the selected devices to be manually controlled. ($01)
6.7.2 L
ISTEN
A
DDRESS
G
ROUP
(LAG)
There are 31 (0 to 30) listen addresses associated with this group. The 3 most
significant bits of the data bus are set to 001, while the 5 least significant bits
are the address of the device being told to listen.
1st Data Byte 2nd Data Byte
Valid ValidNot
Valid
Not
Valid
DAV
Source
DIO-8
(composite)
NFRD
Acceptor
NDAC
Acceptor
All
Ready
None
Ready
All
Ready
None
Ready
None
Accept
All
Accept
None
Accept
All
Accept