ZRAM-205 USER'S GUIDE (Nov86a)
Copyright 1986 FBE Research Company, Inc.


The ZRAM-205 is a modification package for the Z-205 memory card which allows thirty-six 256K RAM chips to be installed in place of the existing 64K RAM chips giving one megabyte of bank-switched memory in the form of four banks of 256K each. One 256K bank is used for system memory. A device driver for MS-DOS is supplied which uses the the remaining three banks (768K) as a memory disk.

Installation of the ZRAM-205 hardware consists of plugging in a small circuit card in place of two chips on the Z-205 card and connecting the pin-1's of all of the memory chip sockets together and to the small circuit card. Soldering is required. The modified Z-205 card still uses only one S-100 slot.


The items listed below are supplied with the ZRAM-205 package. Memory chips are not included.

ZRM8605 Circuit Card (Assembled)
ZRAM-205 Distribution Disk
15 inches of Insulating Sleeving
22 inches of #26 Tinned, Solid Bus Wire


Before beginning the installation of the ZRAM-205 package, the Z-205 memory card should be properly configured and installed in the computer. Refer to your Z-205 User's Manual for the locations of the jumpers and DIP switches.

On the Z-205 card, install programming jumpers at J6, J7 pins 2-3, and J7 pins 4-5. Set DIP switch SW1 positions 3, 4, and 7 to the OFF (1) position and all of the other positions to the ON (0) position. Some of the jumpers and switches may already be in the correct position.

If your computer has 64K RAM chips installed on the motherboard, the Z-205 card must start at address 30000H and 192K of memory must be installed on the motherboard. Set DIP switch SW2 (on the Z-205 card) positions 0 and 1 to OFF (1) and all of the other positions to ON (0). A second Z-205 card may be installed at address 70000H and use control port 99H. Only the "first" Z-205 card may be modified with the ZRAM-205 package.

If your computer has 256K RAM chips installed on the motherboard, the Z-205 card must start at address 80000H and 512K of memory must be installed on the motherboard. Set DIP switch SW2 (on the Z-205 card) position 3 to OFF (1) and all of the other positions to ON (0). If you have 768K of memory installed on the motherboard, remove the high bank (U137-U145) of memory chips and set them aside for later installation on the Z-205 card.

Computers with 256K memory chips on the motherboard must be modified to allow access to the Z-205 card installed on the S-100 bus. If your computer has the new-style (or equivalent) motherboard, you must replace the PAL chip at U173 with the ZP173 PAL chip [No longer available.] that you purchased along with the ZRAM-205. If your computer has an old-style motherboard that has been modified with our ZMF100 series, you must change the jumper on the ZMF100 circuit board as described in the ZMF100 installation guide.


A total of thirty-six industry-standard 256K by 1-bit dynamic RAM chips are required. If your computer has 256K memory chips on the motherboard, the RAM chips installed at U137-U145 must be removed. These chips may be installed on the Z-205 card so you will need to obtain only twenty-seven additional chips. The chips should have a speed rating of 150 nanoseconds. This speed is is fast enough for 8 MHz operation.


Installation of the ZRAM-205 package requires soldering a wire to the foil side of the Z-205 card to connect the memory chip socket pin-1's together and to the ZRM8605 card. A low-power soldering iron (about 25 watts) with a small (1/16th inch diameter) tip should be used.

The required soldering is relatively simple but, if not done properly, could permanently damage the Z-205 card rendering it useless. If you choose to install the ZRAM-205 package you must accept any risks associated with the installation. If you do not wish to do so, please return your ZRAM-205 package to the place where you purchased it for a refund. Before starting, cut the insulating sleeving into the following lengths: 31 pieces 5/16th inch long, 2 pieces 11/16th inch long, 1 piece 3/8th inch long, 1 piece 13/16th inch long and 1 piece 3-1/2 inches long.

To modify the Z-205 card, complete the following steps:

  1. Remove the chips at U35 and U150 and set them aside. They will not be used.
  2. Plug the ZRM8605 card into U35 and U150 (see Photograph 1).
  3. Install the Z-205 card in the computer and verify that it functions normally.
  4. Remove all of the 64K RAM chips (U53 through U88) and set them aside.
    They will not be used.
  5. Position the card component-side down with the connector "fingers" facing
    towards you.

Photograph 1 - The ZRM8605 Installed

In the following steps, the wire will be soldered to the memory chip socket pin-1 pads. When making the connections, simply lay the wire against the pad and flow enough solder onto the joint to make a good connection. In between connections, install the appropriate length of insulating sleeving. Refer to Photograph 2 for details. Be careful to not mistake another nearby pad for a pin-1 pad.

  1. Starting at U61, solder the wire to the pin-1 socket pads in this sequence:
  2. Install the 3-1/2 inch length of sleeving up to U62 and route the free end of the
    wire through the pad labeled P1 on the ZRM8605 card.
  3. Pull the wire so that the sleeving is snug and solder it at P1. Cut off the excess
    wire and save it for later.
  4. Pinch the wire around the edge of the Z-205 card as shown in Photograph 3 to
    pull the wire flat against the Z-205 card.
  5. Starting at U70, solder the remaining wire to the pin-1 pads in this sequence:
    U67--U66--U65--U64--U63--U62 (Note: There are two connections at U62)
  6. Check your work. Make sure that that the wire is connected to all of the pin-1
    pads and not to any other pads. Position the sleeving to insulate the wire from
    any pads that it crosses.

Photograph 2 - View of Wire from Back of Card

In the following step you will install the 256K memory chips. These chips may be damaged by static electricity. Handle the chips as little as possible during installation. When installing a memory chip, be careful that none of the pins of the chip "roll under" or "bend out" of the socket. Also, be sure that the chip is oriented properly, with the pin-1 end towards the pin-1 designation marked on the Z-205 card. The pin-1 end of the chip is indicated by a notch, stripe, or dot on the top of the chip.

  1. Turn the Z-205 card over and install the thirty-six 256K RAM chips.

This completes the modification of the Z-205 card. Install the card in the computer and verify that it still works properly. If not, refer to the IN CASE OF DIFFICULTY section below.

Photograph 3 - Detail of Pinch


The memory disk software supplied with the ZRAM-205 package is usable only with the MS-DOS operating system, version 2.x or later, and will not work with the ZDOS operating system.

To install the memory disk device driver, complete the following steps:

  1. Copy the file ZRAM205.DVD from the distribution disk to your bootable system disk.
  2. Add the following line to your CONFIG.SYS file on your bootable system disk:
    where 'X' is a single digit determined by the starting address of your Z-205 card:
    3 for 30000H (192K), 4 for 40000H (256K) or 8 for 80000H (512K). If X is
    omitted, 8 will be assumed.

This completes the installation of the memory disk device driver. To activate the memory disk, reboot the computer. When MS-DOS installs the driver, a message will appear on the screen telling you which drive letter has been assigned to the memory disk.


If your Z-100 is equipped with a Gemini or EasyPC emulator card and has 256K RAM chips on the motherboard, the Z-205 card must start at address 40000H (256K) if the RAM disk software supplied with the ZRAM-205 is to work properly in the PC mode. To select this starting address, set DIP switch SW2 (on the Z-205 card) position 2 to OFF (1) and all of the other positions to ON (0). If you have 768K of memory installed on the motherboard, remove the "middle" bank (U117-U125) of memory chips and set them aside for later installation on the Z-205 card.

If your Z-100 has a new-style (or equivalent) motherboard, you must replace the PAL chip at U173 with our ZP173A PAL chip.

If your Z-100 has an old-style motherboard modified with our ZMF100A package, you must modify the ZMF100A and replace the PAL chip at U173 (on the ZMF100A) with our ZP173ZMF PAL chip. If your motherboard is modified with our ZMF100, upgrade to the ZMF100A.

To modify the ZMF100A, follow these steps:

  1. On the back of the ZMF100A circuit board, cut the trace going to pin-1 of U173.
  2. Solder a wire from pin-1 of P173 to pin-1 of U173.


Check that none of the pins on the memory chips you installed have "rolled under" or "bent out" of the socket. Look very closely because a "rolled under" pin can be very hard to locate.

Check for bad sockets. On the memory chips that you installed, carefully inspect the point of contact between the pin on the chip and the spring contact in the socket. Use a magnifier if possible. The socket spring contact will sometimes stick open and fail to make contact with the pin of the chip.

Check the pin-1 wire. Make sure that it is properly connected to each pin-1 and is not contacting any other circuits. Check the ZRM8605 card. Make sure that it is properly installed and that none of the header pins are broken off.


The Z-205 memory board was designed to operate at 4.77 MHz. Most boards will work okay at 7.5 or 8 MHz but some will cause WILD INTERRUPT or other error messages to appear during or shortly after bootup. If your board has problems like this, try adding a wait state. Do this by moving the jumper at J6 to J5. This is most often successful on "new" motherboards at 8 MHz.

If adding a wait state doesn't cure the trouble, try replacing "slow" chips with faster ones as shown in the table below. A kit of these chips (part number SK-205) is available from FBE for $12.00 (shipping included). [No longer available.]

Location Present Replacement
U2 74LS244 74ALS244
U3 74LS244 74ALS244
U11 74LS04 74S04
U14 74LS74 74ALS74
U24 74LS175 74F175
U44 74LS244 74ALS244
U45 74LS244 74ALS244
U46 74LS244 74ALS244

Finally, if the problem persists, replace the Delay Line at U20 with a "faster" version. A suitable replacement (part number DDL-175) is available from FBE for $17.50, shipping included. [No longer available.]


FBE Research Company, Inc. warrants to the original purchaser of a ZRAM-205 package that, for a period of 120 days from the date of purchase from FBE Research Company, Inc. or an Authorized Dealer, the ZRM8605 card and software described herein shall be free of defects in material and workmanship under normal conditions of use and service. During this period, if a defect should occur, the ZRM8605 card or software may be returned to FBE Research Company, Inc., for repair or replacement, at our option. No statements regard€ing the ZRAM-205 package performance or suitability for use shall be considered part of this warranty. This warranty becomes null and void if the ZRM8605 card or software is misused, altered, neglected or otherwise abused. There are no other warranties express or implied.


FBE Research Company, Inc., accepts no responsibility, obligation, or liability for damages including but not limited to loss of profits or benefits arising from or consequential to the use or misuse of the ZRAM-205 package.


Z100 and ZDOS are trademarks of Zenith Data Systems, ZRAM-205 is a trademark of FBE Research Company, Inc. and MS is a trademark of Microsoft Corporation.

[Converted from an old word processor format June 30, 2000. For historical purposes only. Some newly added material follows.]


The ZRM8605 is so simple that there was never a "proper" schematic drawn. The circuit board consists of two header-plugs, two sockets and a 74LS157 chip. See Photograph 1 for the layout. The headers are wired pin-for-pin to the adjacent sockets. The 74LS157 is wired to the sockets-headers as shown in the hand drawn sketch shown below. The sketch was found in the ZRAM-205's file folder.

Authentic, 1986-vintage, sketch.