Difference between revisions of "MX15-B Memory Multiplexer"
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The '''MX15-B Memory Multiplexer''' was part of the [[UNICHANNEL 15 System]], which allowed a [[PDP-11]] (usually a [[PDP-11/05]]) to act as a [[front end]] for a [[PDP-15]]. | The '''MX15-B Memory Multiplexer''' was part of the [[UNICHANNEL 15 System]], which allowed a [[PDP-11]] (usually a [[PDP-11/05]]) to act as a [[front end]] for a [[PDP-15]]. | ||
| − | The MX15-B allowed the PDP-11 (both the [[Central Processing Unit|CPU]], and [[Direct Memory Access|DMA]] devices on the PDP-11's [[UNIBUS]]) access to | + | The MX15-B allowed the PDP-11 (both the [[Central Processing Unit|CPU]], and [[Direct Memory Access|DMA]] devices on the PDP-11's [[UNIBUS]]) access to PDP-15 [[main memory]] attached to the MX15-B, and also allowed the PDP-15 CPU access to both the PDP-11's memory, and that PDP-15 memory - i.e. it turned both memories into [[shared memory]]. |
| − | Some DMA devices on the UNIBUS (such as the [[RK11 disk controller#RK11-E|RK11-E]]) were able to do 18-bit transfers over it; they used the two UNIBUS parity lines for the two extra data bits of the 18-bit PDP-15. The two extra bits were not used by the PDP-11 or its memory, but went straight through the MX15-B, directly to the PDP-15's memory. | + | Some DMA devices on the UNIBUS (such as the [[RK11 disk controller#RK11-E|RK11-E]]) were able to do [[UNIBUS parity#18-bit width|18-bit transfers]] over it; they used the two UNIBUS [[parity]] lines for the two extra data bits of the 18-bit PDP-15. The two extra bits were not used by the PDP-11 or its memory, but went straight through the MX15-B, directly to the PDP-15's memory. |
The MX15-B included an [[arbiter]], so that when the PDP-15 and PDP-11 (both of which are [[asynchronous]]) tried to interact with memory at the same time, a choice was made; the PDP-15 was given priority. | The MX15-B included an [[arbiter]], so that when the PDP-15 and PDP-11 (both of which are [[asynchronous]]) tried to interact with memory at the same time, a choice was made; the PDP-15 was given priority. | ||
| − | Memory addresses in the PDP-11 (which uses byte addressing) were converted to PDP-15 word addressing by dropping the low | + | Memory addresses in the PDP-11 (which uses byte addressing) were converted to PDP-15 word addressing by dropping the low bit, and conversely for transfers in the other direction. It also converted DATIP and DATOB type UNIBUS cycles (which have no exact equivalents in the PDP-15's memory system) to PDP-15 memory operations with the same effect. |
| + | |||
| + | ==External links== | ||
| + | |||
| + | * [http://bitsavers.org/pdf/dec/pdp15/XVM/DEC-15-HUCMA-B-D_UC15_Nov73.pdf UNICHANNEL 15 System Maintenance Manual] (DEC-15-HUCMA-B-D) - the MX15-B is covered in detail in Chapter 4 | ||
| + | * [http://bitsavers.org/pdf/dec/pdp15/XVM/UC15_schematics_Aug76.pdf UC15-0 Engineering Drawings] - the MX15-B is covered on pp. 18-44 of the PDF | ||
| + | |||
| + | [[Category: PDP-15s]] | ||
| + | [[Category: UNIBUS Machine Interfaces]] | ||
Latest revision as of 23:35, 30 November 2022
The MX15-B Memory Multiplexer was part of the UNICHANNEL 15 System, which allowed a PDP-11 (usually a PDP-11/05) to act as a front end for a PDP-15.
The MX15-B allowed the PDP-11 (both the CPU, and DMA devices on the PDP-11's UNIBUS) access to PDP-15 main memory attached to the MX15-B, and also allowed the PDP-15 CPU access to both the PDP-11's memory, and that PDP-15 memory - i.e. it turned both memories into shared memory.
Some DMA devices on the UNIBUS (such as the RK11-E) were able to do 18-bit transfers over it; they used the two UNIBUS parity lines for the two extra data bits of the 18-bit PDP-15. The two extra bits were not used by the PDP-11 or its memory, but went straight through the MX15-B, directly to the PDP-15's memory.
The MX15-B included an arbiter, so that when the PDP-15 and PDP-11 (both of which are asynchronous) tried to interact with memory at the same time, a choice was made; the PDP-15 was given priority.
Memory addresses in the PDP-11 (which uses byte addressing) were converted to PDP-15 word addressing by dropping the low bit, and conversely for transfers in the other direction. It also converted DATIP and DATOB type UNIBUS cycles (which have no exact equivalents in the PDP-15's memory system) to PDP-15 memory operations with the same effect.
External links
- UNICHANNEL 15 System Maintenance Manual (DEC-15-HUCMA-B-D) - the MX15-B is covered in detail in Chapter 4
- UC15-0 Engineering Drawings - the MX15-B is covered on pp. 18-44 of the PDF
