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National Instruments Corporation
7
GPIB ASIC Reference Manual Errata
Appendix A
Insert the contents below to create a new section following the
System
Configuration
section on Page D-9 of the
TNT4882 Programmer Reference
Manual
.
Operation
Configuring the System Cable Length
To use HS488 transfers, a Controller sends the CFE command followed by
a CFGn command.
Responding to System Cable Length Configuration
HS488 devices (including the Controller) must recognize and respond to
the system cable length commands (CFE and CFGn). The software must
recognize the CFE and CFGn commands and implement the CF interface
function. Unlike other GPIB commands, the TNT4882 does not
automatically respond to these commands. The software must assist the
hardware.
To implement the CF interface function set AUXRB[CPT_ENABLE] and
IMR1[CPT IE] to interrupt on undefined commands.
ISR1[CPT] sets when an undefined “primary” command is received. When
an undefined primary command is received, CPT also sets on all secondary
commands until a defined primary command is received. Each time the
ISR1[CPT] sets, execute the following algorithm:
1.
Read the command byte from the CPTR
2.
If the command is CFE (0x1F) then
a.
Disable HS488 as described in the following section
Disabling
HS488
b.
Write 0xDF to AUXRF to hold off on all commands
3.
Otherwise, if the command is a PCG command other than CFE then
a.
Write 0xD0 to AUXRF to clear hold off on all commands
b.
Clear AUXRB[CPT_ENABLE], then set
AUXRB[CPT_ENABLE]
4.
Otherwise, if (0x61
≤
command
≤
0x6F)
a.
Subtract 0x60 from command to calculate cable length
b.
Enable HS488 with Cable Length as described in the following
section,
Enabling HS488
5.
Write AUXMR[VALID] to release DAC hold off
