#14 Allow 127 as secondary address
The constant gpib_addr_max = 30 (0x1E) is used to limit the range of both the primary and the secondary addresses. This is consistent with National Instrument GPIB documentation.
While that is always true for the PAD (31 is reserved for universal commands), it is not always true for the SAD where 127 (= 96 + 31 respectively 0x60 + 0x1F) is a valid address. At least it was in earlier HP-IB days.
For reference, two versions of the HP-IB Tutorial (in one the PAD is mentioned, in the other one the SAD)
and the HP 9121D/S command set where 0x1F is used to initiate the selftest.
HPIB_tutorial_HP.pdf
Tutorial Description of the Hewlett-Packard Interface Bus
Page 23
2.6.4 Secondary Commands
Secondary Commands consist of the ASCII characters 96-127 decimal.
hp-ib_tutorial_1980.pdf
5952-0 Tutorial Description of the Hewlett-Packard Interface Bus
Page 60
Regarding the IEEE-488/ANSI MC1.1/IEC 625-1 standards
There are 31 available primary Talk and Listen addresses. 0-30 are
available, 31 is reserved for the Universal Untalk and Universal Un-
listen commands.
HP Flexible Disc Drive Command Set
Appendix A
Page A-6
Command Table
8290X Compatible Commands
See also
#9 max address error
https://sourceforge.net/p/linux-gpib/bugs/9/
Thanks for this patch.
Applied 4dce09
-Dave