Difference between revisions of "QBUS ROMs"
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<!-- In all of the cards, the entire ROM contents were not directly visible on the QBUS, but through a window, unlike later, larger [[QBUS]] ROM cards. --> | <!-- In all of the cards, the entire ROM contents were not directly visible on the QBUS, but through a window, unlike later, larger [[QBUS]] ROM cards. --> | ||
| + | ==Use restrictions== | ||
| + | |||
| + | Note that in the [[LSI-11 chip set|LSI-11]] [[microprocessor]], several [[instruction]]s use a [[QBUS#Signalling|DATIO bus cycle]] to fetch source [[operand]]s from [[main memory]]: | ||
| + | |||
| + | * MTPS | ||
| + | * MUL | ||
| + | * DIV | ||
| + | * ASH | ||
| + | * ASHC | ||
| + | |||
| + | Use of these instructions with an ''operand'' in ROM, in ROM code which is to run on any of these processors, is thus not possible. This is, of course, easily avoided by loading the operand into a [[register]] first. | ||
{{semi-stub}} | {{semi-stub}} | ||
[[Category: QBUS ROMs]] | [[Category: QBUS ROMs]] | ||
Latest revision as of 12:58, 5 July 2023
DEC produced several generations of QBUS ROM cards, initially specialized to a bootstrapping use. Those early ones also included QBUS terminators; some of the later were multi-function cards, and included other functionality.
- The first was the REV11 DMA Refresh/Bootstrap/Terminator dual card.
- The second was the BDV11 Bus Terminator/ROM, a quad card.
A number of ROM memory cards were also available:
- MRV11-A Read-Only Memory Module (also known as the 'MRV11)
- MRV11-B UV PROM-RAM Memory Module
- MRV11-C Read-Only Memory Module
- MRV11-D Universal Programmable Read-Only Memory
Multi-function cards which included ROMs included:
Use restrictions
Note that in the LSI-11 microprocessor, several instructions use a DATIO bus cycle to fetch source operands from main memory:
- MTPS
- MUL
- DIV
- ASH
- ASHC
Use of these instructions with an operand in ROM, in ROM code which is to run on any of these processors, is thus not possible. This is, of course, easily avoided by loading the operand into a register first.
