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IEEE-488 Programming
3-8
3.2.6 EOI and bus hold-off modes (K)
Purpose
To program EOI and bus hold-off modes.
Format
K0
Send EOI with last byte; hold off bus until commands processed on X
K1
Do not send EOI with last byte; hold off bus until commands processed on X
K2
Send EOI with last byte; do not hold off bus on X
K3
Send no EOI with last byte; do not hold off bus on X
Default
Upon power-up, or after receiving a DCL or SDC command, the K0 mode will be enabled (both
EOI and bus hold-off enabled).
Description
The K command allows control over whether or not the instrument sends the EOI command at
the end of its data string, and whether or not bus activity is held off (through the NRFD line)
until all commands sent to the instrument are internally processed once the instrument receives
the X character.
The EOI line on the IEEE-488 bus provides a method to positively identify the last byte in a
multi-byte transfer sequence. Keep in mind that some controllers rely on EOI to terminate their
input sequences. In this case, suppressing EOI with the K command may cause the controller
input sequence to hang up unless other terminator sequences are used.
The bus hold-off mode allows the instrument to temporarily hold up bus operation when it re-
ceives the X character until it processes all commands sent in the command string. The purpose
of the hold-off is to ensure that the front end FETs and relays are properly configured before
taking a reading. Keep in mind that all bus operation will cease–not just activity associated with
the Model 6512. The advantage of this mode is that no bus commands will be missed while the
instrument is processing commands previously received.
The hold-off period depends on the commands being processed. Table 3-3 lists hold-off times
for a number of different commands. Since NRFD hold-off is employed, the handshake se-
quence for the X character is completed.
NOTE: NRFD will be held off until each byte is recognized (1-60msec in continuous trigger
mode; 1msec in one-shot trigger mode).
Table 3-3
Bus hold-off times
Commands
Bus held off on X until:
L
F, R, C
Z, N
All others
NVRAM storage completed (13msec)
6512 front end configured (20msec)
Value taken (360msec)
When X is recognized
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