The Memory Adapter with the optional 8087 Option pictures I originally uploaded, could be different then the
ones that BIGFIX provided in there uploaded documentation. Some boards have a 541634-X-X-cX number.
..
For those forum users that are following this set of messages just so you know that the file pc100a-ma-dwg-2-pdf, contains two
circuit schematic diagrams but only one component layout for both schematics.
..
The Memory Adapter with out the 8087 NPU option on board should use fewer logic gates then the one with the 8087 NPU installed.
A part number with a C1 is without the 8087 installed and a C2 has the 8087 installed.
..
The document that user BigFix upload is Documentation Number 546535-0-0BP2 rev A with dates form 04-Apr-1984 and the release date of 15-June-1984. If you look at page 1 of this documentation you will see that there has been some revisions. The Etched Circuit Board is listed as a rev. B1 and is for DEC. PN 5016534-01 but the PCB component layout is (UA) 5416535-0-0A that this file contains.
..
It could be some thing like this:
As far as IC E5, E6, E11 and E17 are present in the part list but are not on the schematic likely means a different PCB board with a different circuity being used. When DEC originally designed the Rainbow 100 computer they put the Intel 8088 that is on its motherboard in Minimum Mode. To use the 8087 NPU/FPU/APU in minimum mode and/or with a Z80 microprocessor will take some extra support logic to work.
..
Dec part # 9009185-00 is not used but it was still noted in the part list.
E5 is an 74F08 AND gate Quad
E6 is a 74F00 NAND gate Quad
E11 is a 74LS74 FF-D Dual Edge Triggered.
E17 is unknown
..
As far as extra logic gates. (Some 3 RD parity NPU adapter boards also do this as well)
There was likely hardware wired on the board so MS-DOS would automatically detect the NPU as being available (regardless of what the BIOS states about it). You would have to look up the memory location that older versions of MS-DOS check for it. (Likely, some where in the private memory spaces IO Vector and its relocation table addressing).
..
Other possible issues.
Print Errors in the documentation for DEC, there also could be other versions of the board out there that there is no current data
available for it.
..
You might have to manually compare BIGFIXs schematics with the Component layout that is with it and delete the unused logic devices
on a copy of there set. This would let you confirm what you are looking at. You could also try to directly bread board a evaluation unit off those schematics and then test it.
..
The standard IBM PC and PCXT use the following addresses for the NPU addressing (in Hex format)
0F0 Clears Math Coprocessor Busy Signal
0F1 Resets Math Coprocessor
---------------------------------------
0F2 reserved
0F3 reserved
0F4 reserved
0F5 reserved
0F6 reserved
0F7 reserved
* 0F8 to 0FF Math coprocessor Addressing
---------------------------------------
0F8 Opcode Write to NPU, Read CW or SW register from NPU
0F9 Reserved for upper byte access in 8 bit systems
OFA Write Data to NPU or READ data from NPU
OFB Reserved for upper byte data access in 8 bit systems
OFC Write Exception Pointers or Read Exception Pointers (for none Intel)
OFD Reserved for upper byte access of Exception Pointers in 8 bit systems
OFE Read Opcode Status All or Write Opcode Status (for none Intel)
OFF Reserved for upper byte access of Opcode Status access in 8 bit systems
============================================================================
..
IBM 5155 5160 PCXT models register address coinsuring NMI signal use (In hex).
Port Address:
62 input Bit 1 +CoProcessor Installed
===== Bit 6 + I/O Channel Check
===== Bit 7 +RAM Parity Check
61 Out Bit 4 -Enable RAM Pariy Check
==== Bit 5 -Enable I/O Channel Check
==== Bit 6 -Hold Keyboard Clock Low
==== Bit 7 - Enable Keyboard or + Clear Keyboard
..
A0 to AF NMI Mask Control Register (XT only)
that is from 160 in dec. or 10100000 in binary to 175 in dec. or in binary as 10101111.
..
IBM PCXT System BIOS 8088 Software Interrupts theats a NMI interrupt like this :
Int. 02 Address 8B NonMaskable uses BIOS Entry of NMI_Int. So on systems that have no 8087 routeteens in the BIOS firmware
they are hard coding the 8087 interrupt in logic circuits.
..
The DEC. Rainbow 100 Computer uses those address (61,62, and A0 to AF) above for different hardware.
Might have to dissemble a newer version of Cold Blue for the Rainbow 100 computer and the MS-DOS 2.00 support utilities for the
computers 8087 to get the Vector table location for the 8087 and its data bit used, if all else fails.
..
Hopefully this messages help explain what pins 13 and 9 of IC 1 the I/O QA decoder circuit are used for that is not shown on the schematic provided by BIGFIX.