sean caron > ROLM CBX 7000/8000 visual field guide

ROLM CBX 7000/8000 visual field guide

The following page aims to provide a visual reference and identification guide to ROLM CBX 7000/8000 boards. All boards on this page are indexed by ROLM M/N and when available, the description etched on the board. Interesting circuit features are called out where possible. Click on the picture of any board for an extra large version!

This is by no means (yet) an exhaustive list of CBX 7000/8000 boards. I personally have a few new ones to photograph, and there are many yet that I do not own. I hope to occasionally add new board photos and I will gratefully accept photo submissions!

Examining the various boards that compose the CBX provides insight as to the nature of the system architecture and prompts questions as to the deeper nature of same. Note in particular the use of the AMD AM2504 12-bit successive approximation register on the channel coder cards. Internally, the ROLM CBX 7000/8000 used 12-bit, 12 kHz PCM which vastly complicated the task of interfacing them with standard, 8-bit 8 kHz (G.711 u-law) DS1 trunks. This complication (and the delayed, expensive, high-board-count DS1 interface that resulted) is cited as one of the primary reasons for the long-term failure of ROLM and the CBX architecture in the PBX marketplace.

As well, note the use of four AMD AM2901 4-bit ALU slices and the large number of PROMs in the CBX central processor. Clearly the CBX was a 16-bit microcode machine, an architecture similar to many contemporary minicomputers of the era. Considering that ROLM's original line of business was producing mil-spec implementations of the Data General NOVA mini, one wonders how closely the architecture of the CBX might be related to that of the NOVA.

ROLM made extensive use of small microprocessors throughout the common equipment, line and trunk cards of the CBX. Most typical appears to have been the Zilog Z80 and variants, though the occasional Intel micro will show up from time to time. Even the very small SCBX that was the subject of this photo study contained almost ten contemporary personal computers worth of microprocessors in addition to the primary microcoded bit-slice CPU!

You can learn more about the ROLM CBX 7000/8000 machines by perusing Vol. 2 of the System Service Manual here. The document was scanned by a Konica Bizhub MFP (I helped) and was graciously supplied for scanning by Dennis Hock.

If you can provide a copy of Vol. 1 of the CBX 8000 System Service Manual, even temporarily, such that it may be scanned and preserved for posterity, please contact me!

	8508 REAL TIME CLOCK
	8550 EXPANDER CARD (ONE EXPANDER CARD PER SHELF) NOTE JUMPER PACK CONFIGURES SHELF NUMBER 2X TI SN74154 4-TO-16 DEMULTIPLEXER
	8551 16 CHANNEL CODER AMD AM2504 12-BIT SUCCESSIVE APPROXIMATION REGISTER FAIRCHILD F74154 4-TO-16 DEMULTIPLEXER
	8552 16 CHANNEL DECODER
	8554 8 CHANNEL ANALOG LINE INTERFACE An old, early 8-channel analog line interface. Interestingly, there are no relays on this board! Note the discrete transistors. Perhaps they attempted a solid state approach instead of line relays?
	8567 ETI BOARD 2 This was one of two boards to drive a group of 8 ETI (digital) sets, a precursor to the ROLMphone. This appears to be more the physical layer of the ETI interface. Not much logic here.
	8601 CONFERENCE BRIDGE 2 16X AMD AM27S02 64 BIT INVERTING OUTPUT BIPOLAR RAM This is probably the data store portion of the conference bridge module.
	8605 ROTARY REGISTER TI SN74154 4-TO-16 DEMULTIPLEXER 10X AMD AM27S02 64 BIT INVERTING OUTPUT BIPOLAR RAM
	8606 ROTARY SENDER 5X AMD AM27S02 64 BIT INVERTING OUTPUT BIPOLAR RAM
	8607 QUAD DTMF 4X ROCKWELL CRC8030 DUAL TONE DECODER 8X ITT NORTH AND AMS GROUP FILTERS The signal flow begins with the group filters, which are basically just band pass filters tuned for DTMF. The signal then hits the tone decoders which will have specified outputs on a series of data pins for each possible DTMF digit. The data is passed back into the PBX for further processing.
	8608 CONFERENCE BRIDGE 1A Lots of random discrete logic, most likely ROLMbus interface and control functions for the conference bridge.
	8760 2 CHANNEL SERIAL DEVICE INTERFACE NOTE JUMPER PACK CONFIGURES DEVICE ADDRESS 2X GI AY-5-1013 UART MOTOROLA MC6860 DIGITAL MODEM
	75080 TDM NETWORK CONTROL-TCC 4X MK4801 1K X 8 BIT SRAM The outstanding feature here is the block of SRAM, which was likely the data store for the TDM bus.
	77300 TONE SENDER 3X UNKNOWN PROM (?)
	85360 FLOPPY DISK INTERFACE SGS Z8400 (ZILOG Z80) MICROPROCESSOR 4X INTEL D2716 2K X 8 BIT UV EPROM NATIONAL INS1771 FLOPPY DISK CONTROLLER INTEL 8253 PROGRAMMABLE INTERVAL TIMER The use of a COTS FDC is encouraging, implying that it might not be too hard to read diskettes from the CBX 8000 in another 8" drive for backup and analysis.
	85510 8 CHANNEL DID TRUNK The large brushed metal cans are transformers and they contribute significantly to the weight of the board. Mostly physical layer for interface with 2 wire DID POTS trunks.
	85540 8 CHANNEL ANALOG LINE INTERFACE This appears to be an updated version of the 8554 interface. Note the inclusion of line relays in this later iteration of the card. All interfaces of this type follow a basic pattern to implement the BORSCHT functions regardless of PBX manufacturer. You will see gross similarities in analog line cards of any make. The majority of analog line interfaces (and line cards in general) in my CBX 8000 are of this type.
	85562 ATTENDANT CONSOLE INTERFACE OKI M80C51 (INTEL 8051) MICROCONTROLLER On one side, there is clearly all the circuitry for handling one channel of audio for the operator position. On the other, a microcontroller interfaces to the rest of the PBX and provides support for the advanced functionality of the operator position.
	85620 UNIVERSAL TRUNK CONTROL INTEL 8048 MICROCONTROLLER 5X INTEL 8243 MCS-48 I/O EXPANDER 24X TI TIL117 PHOTOTRANSISTOR OPTOCOUPLER
	85640 4 CHANNEL DIRECT TRUNK LOGIC
	85660 ETI BOARD 1 ZILOG Z8400 (Z80) MICROPROCESSOR 2X MOTOROLA MCM2708 1024 X 8 BIT UV EPROM This was one of two boards to drive a group of 8 ETI (digital) sets, a precursor to the ROLMphone. Board 1 seems geared more towards control and protocol, while the physical layer is implemented more on BOARD 2.
	86020 BIAS GENERATOR
	86070 QUAD DTMF APPEARS TO BE UPDATED VERSION OF 8670 4X ROCKWELL CRC8030 DUAL TONE DECODER 8X AMS AND CERMETEK GROUP FILTERS
	86130 SINGLE SUPPLY MEMORY 256K 84X TI TMS4164-20NL 64K X 1 BIT ASYNCHRONOUS PAGE MODE DRAM (200 nS) This board can tell us a lot about the architecture of the CBX 8000... 256K of memory (and this seems a minimum for the platform) implies that the CPU must have at minimum 18-bit addressing, or be using some sort of bank-switched scheme... The number of DRAMs implies the labeling of 256K is likely 256 kW, with a 16-bit word, not 256 kB.... As well, some sort of parity or error correction scheme is in likely in use here as well...
	86200 8000 MEMORY CONTROLLER INTEL D8740N UNKNOWN EPROM (?) 2X MMI PAL16R8CN 8X8 PROGRAMMABLE ARRAY 2X SIGNETICS N82S123N 256 BIT TTL BIPOLAR ROM If I had to take a guess at it, this is probably address decode and other glue...
	86240 8000 CPU A 4X AMD AM2901 4 BIT SLICE ALU 1X SIGNETICS N82S181 1K X 8 BIT PROM The heart of the common control appears to be a 16-bit CPU expressed in microcode...
	86250 8000 CPU B 7X SIGNETICS N82S181 1K X 8 BIT PROM Obviously mostly a microcode store for CPU A...

All photographs courtesy of Russell Dekema

home