Expanding The MVME201 To 1 Megabyte

Ray Robinson

Speech Research Centre

Macquarie University

North Ryde 2113

NSW Australia

INTRODUCTION

The MVME200 is a VME bus 64k byte memory card made by Motorola. The MVME201 is the same card, but with 256k byte capacity, due to 64Kx1 DRAMS (Dynamic RAMS) being used instead of 16Kx1 DRAMS. My VME bus system needed more memory, so I upgraded the card to 1M byte by using 256Kx1 DRAMS. Heres how I did it. I call it the MVME201-1.

ADDRESS

The memory is arranged physically as 2 banks of 18 chips each (36 total), giving a 16 bit word and 2 bits of parity. These 2 banks are arranged as 4 pages of memory 16 bits wide and individually addressable by 4 base address patch areas. The size of the page is set by the DRAMS used, 16K for 4116 (16Kx1), 64K for 4164 (64Kx1), and 256K for 41256 chips (256Kx1). To modify the base address selection for 256K pages, add eight 10K resistors to the gates U45, U51, U55, and U59 on the Figure 5-2 sheet 4 of the MVME200/201 users manual. Also see Diagram 1 (below).

REFRESH

The 256Kx1 DRAMS require identicle refresh to the 64Kx1 DRAMS and so no modifications are required.

MULTIPLEXING

The MVME200 multiplexes 14 address lines to 7 for the 16Kx1 DRAMS. The MVME201 multiplexes 16 address lines to 8 for 64Kx1 DRAMS. For the 256Kx1 DRAMS, we need 18 address lines multiplexed to 9. To add the mux for MA8 (the 9th address line to the 256Kx1 DRAMS), I used 3 spare gates and added 2 resistors. The address lines LA16 and LA17 are gated with signal 100A and 100A* (an inverted 100A signal), by U80 and U81. U81 needs a 1K pullup resistor. The outputs from these 2 gates go to U69 and then through a 22 ohm matching resistor to the MA8 address line on the DRAMS (pin 1 or called VBB on 16Kx1 DRAMS). See Diagram 2 below. The signals 100A and 100A* are found on Figure 5-2 sheet 6 of the MVME200 /201 users manual. The address lines LA16 and LA17 are on sheet 5. The destination for MA8 is on sheets 2, 8, and 9.

PROCEDURE

Remove 36 DRAMs. I added the 8 address pullup resistors to U65, U51, U55, and U59, by neatly soldering them on the component side of the board, from the appropriate pin to pin 16 (VCC) of the same chip. I did the same for the pullup resistor on U81 in the new mux. The spare gates on U80, U81, and U69 where checked with a multimeter to find out which pins were earthed. These were cut and bent under the chip as in Diagram 3 and checked again for any short circuits. Some black wirewrap wire was threaded neatly under chips and soldered directly to the pins of the gates, again on the component side of the board. One end of the 22 ohm matching resistor was soldered to the jumper W4 which is located near the front panel. Add eighteen 256Kx1 DRAMS (150ns) to U1, U6, U11, U13, U18, U20, U24, U26, U31, U36, U38, U42, U46, U48, U52, U56, U60, and U62. They are $7 each in Australia.

PATCHING

Ensure the patches W5 and W2 are in, and W3, R6, W4, and W1 are open (Figure 5-2 sheet 2 MVME200/201 Users Manual). These configure the DRAMS and are located near the front panel. The 22 ohm resistor from the new mux (MA8) goes to the junction of R6 and W4. The 4 memory pages are set with patches J2, J3, J4, and J5. Diagram 4 shows J2 patched for a base address of 000000 HEX and J3 for 040000 HEX. The other 2 pages (set by J4 and J5) are shown disabled. After testing, the extra 1/2 megabyte can be plugged in and enabled. The other patches should remain unchanged. They are (as factory set) J1, J7, and J8 connected, and J6 open.

ERRORS

There are bypass capacitors on the old VBB line, now MA8 address line. They are C5, C14, C15, C25, C27, C38, C47, C54, and C61. Find these and remove them. Not all may have been fitted. Figure 5-2 sheet 2 of the MVME200/201 Users Manual wrongly shows all bypass caps on the +5 volt line. Figure 5-2 sheet 5 of the manual shows wrong pin labelling on one of the mux chips U29). It should be U29 pin 3, LA08 and U29 pin 6, LAO9 and U29 pin 10, LA10 and finally U29 pin 13, LA11.

TESTING

The board was tested in my system, with the MVME101BUG monitor commands BI to initialise the RAM and BT to block test it from 10000 to 7FFFE. If the new mux (MA8 address line) is not working properly you will find you have only 64K of RAM with images throughout this range. If so, look for one of those bypass caps on the MA8 address line. The address space 0000 to FFFF is used onboard by the MVME101 CPU and so the RAM on this card in that area is unused. If all went well, you now have 1/2 a megabyte of RAM up to 80000 HEX. You can now boot VERSADOS and run SYSGEN and ASSEMBLER. I chose not to fit the other 1/2 megabyte of RAM until I need it. All you have to do 18 fit the chips and set the base address with J4 and J5 and the whole 1 megabyte is ready.