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How to build a Syntor® PROM to EPROM/EEPROM adapter.

USEFUL FOR PROM REPLACEMENT:

This adapter can be used simply to allow the replacement of the Syntor® PROM (obsolete, hard to find, expensive when found) with an EPROM or EEPROM, with no change in the number of channels available, etc. In this case, use of the adapter is 100% compatible with all the normal Motorola Syntor® control heads, accessories and cables. The Syntor® can be programmed for up to 32 channels when used with standard Motorola control heads and accessories.

USEFUL FOR EXPANDING THE NUMBER OF CHANNELS AVAILABLE:

This adapter can also be used to expand the number of channels which can be "programmed" into the Syntor® radio.

It is fairly easy to modify a 16 channel control head, expanding the concept of the talkaround switch used in the normal 32 channel control head to a "bank" switch, so that up to 16 banks of 16 channels each are available. This arrangement provides the Syntor® radio with up to 256 channels selectable via the control head and bank switch. The bank switch can be conveniently mounted close to the control head. Minor modifications to the Syntor® radio (besides the addition of the PROM to EPROM adapter) are necessary to use the adapter with more than 32 channels.

The bank switch concept is also applicable to 4 and 8 channel radios (i.e. radios using 4 or 8 channel control heads), but is more difficult to implement.

COMPATIBLE WITH A LARGE VARIETY OF EPROMS AND EEPROMS:

This adapter was designed to be very flexible and can be used with a large variety of EPROMs (including all 2716 through 27512 varieties) and EEPROMs (including 2804 thru 28256 varieties). It will work with most 24 or 28 pin EPROMs or EEPROMs. Not all devices will provide the full 256 channels. The capacity of smaller EPROMs or EEPROMs is not adequate for 256 channels so the channel capability reflects the size of the device used. To obtain 256 channel capacity a 2732 or larger EPROM is necessary.

It accommodates the large variety of devices by means of some minor wiring changes. See the table below for details.

AVAILABLE SOFTWARE:

Software is available that allows you to easily generate the PROM data needed to program the various EPROMs, and EEPROMs that can be used with this adapter. The software can also be used with normal Syntor® PROMs. The generated data is placed into standard Intel HEX files so that the PROMs, etc. can be programmed with nearly any PROM/EPROM programmer. Programming services are also available from us for those who don't have access to a suitable programmer.

KITS AND ASSEMBLED ADAPTERS ARE AVAILABLE:

While the intent of this article is to provide you with information adequate to allow you to construct your own adapter, it is also possible to purchase assembled adapters, bare circuit boards, and adapter parts kits from us.

DISCLAIMER:

The information provided below is thought to be complete and accurate, but has not been tested for all possible EPROMs, EEPROMs, etc., might contain errors, and is provided free of charge. It is thus provided without warranty or guarantee of any kind. The author specifically disclaims any liability for damage which might occur to the user, EPROMs or EEPROMs, Syntor radio, etc. due the proper or improper use of this information and/or adapter constructed from this information.

MATERIALS LIST for "home-brew" EPROM/EEPROM adapter:

Soldering is required for construction of this adapter, and special care is required to insure that the completed adapter will fit properly into the Syntor® radio. A circuit board only, a kit of parts, and assembled adapters are available that ease the construction difficulty.

It is highly recommended that the prospective builder of this adapter read carefully the entire contents of this article before beginning construction. Note that the EPROM and EEPROM part numbers used here are "generic", with 2764 (for example) including many 2764 variants such as 2764, 2764A, 27C64, 27C64A, 27HC64, etc. There may be other EPROMs or EEPROMs that will also work with this adapter that are not listed here.

Wiring for an adapter circuit which can be used with 24 or 28 pin EPROMs and EEPROMs (2716, 2732, 2764, 27128, 27256, and 27512 type EPROMs, also 2804, 2816 and 2864 EEPROMs, etc.) is shown below. The pin numbers in column 3 ("28 pin nrs") are for a 28 pin socket. A 28 pin socket is recommended as it can be used with either 28 or 24 pin EPROMs, with the 24 pin EPROMs being inserted into the lower 24 pins of the socket. The pin numbers in column 4 ("24 pin nrs") are for a 24 pin socket, which can be used only with 24 pin EPROMs and EEPROMs (2716, 2732, 2804, 2816, etc.).

NOTE: The space available inside the Syntor® radio for this adapter is more than adequate, but requires some careful planning to insure that the completed adapter will fit into the radio without interference from the VCO module, etc.

The tabular data translates to a wiring diagram as follows: The PROM pin shown in the left two columns is connected to the EPROM pin shown in the corresponding appropriate right columns (so PROM pin 12 goes to EPROM pin 11 (or 9), etc.). Note that this adapter circuit is applicable to a large variety of EPROMs or EEPROMs -- but the adapter wiring is NOT THE SAME for all of these different devices. The table below has a variety of wiring differences for the various EPROM and EEPROM devices. MOST of the wiring is the same for all devices, with a minor amount of wiring specific to specific devices. This makes it fairly easy to modify the adapter to work with different devices. The printed circuit board referred to above has a small number of "jumper" wires with allow it to work with any of the listed devices by the simple expedient of changing a few jumper wires.

WIRING TABLE: Note that where more than one connection is listed for a pin (pin 1, 26, 27, etc. of the 28 pin numbers) you will need to select the correct connection according to the type of EPROM you are planning to use.

ADDITIONAL WIRING NOTES:

1.) The D4, D5, D6 and D7 EPROM/EEPROM pins are not used in this application. No connection should be made to these pins.

2.) If the A8 pin is used (i.e. 32 or more channels to be used), there is a jumper inside the radio that must be removed. This jumper (if present) grounds the A8 input to the PROM. Once this jumper is removed, the A8 input to the PROM is controlled by the wiring from the control head (by the "talkaround" switch in the control head or by a "bank switch" switch that has been added to the control head, internally or externally). Note that if this jumper is removed and the control head does not include the extra switch(es) --- then the radio will not operate correctly and may not operate at all. Note: using the A8 pin for channel expansion via the normal control head wiring is ONLY compatible with 16 and 32 channel control heads.

3.) The EPROM address inputs A9, A10 and A11 may be used to expand the bank switching capability to as many as 16 frequency banks (256 channels). These inputs can be connected externally (i.e. NOT through the PROM socket) to the frequency con trol cable and hence to a bank selector switch located next to the control head. If these inputs are not used for bank switching, they should be grounded to pins 8 and 13 of the PROM connector.

4.) If a 24 pin EPROM (2716, 2732) is used (in the 28 pin EPROM socket) then pin 26 of the EPROM socket should be connected to Vcc (pin 16 of the PROM connector). If a 28 pin EPROM (2764, 27128, 27256) is used, then pin 26 of the EPROM socket (A13) should be connected to ground (pin 8 & 13 of the PROM connector).

5.) EPROM address inputs A12, A13, A14 and A15 (if present on the EPROM being used) should be connected to ground (pins 8 and 13) of the PROM connector. These address input are not needed or used when up to 16 banks of 16 channels are used.

6.) Pin 27 of the EPROM is the "program" pin for 2764 and 27128 EPROMs. It is an additional address input A14 for 27256 EPROMs. Connect this pin as shown in the table above for the type of EPROM you will be using.

7.) When EEPROMs are used, the following applies: Pin 23 (of the 28 pin socket) is "write enable" for 28C16 EEPROMs. Pin 27 is "write enable" for 28C64 EEPROMs. Connect this pin as shown in the table above for the type of EEPROM you will be using. Other than this pin, EEPROMs are wired up identically to the closest EPROM type (i.e. 2816 like 2716, 2864 like 2764).

8.) Pin 1 of the EPROM is Vpp (a higher voltage used during programming) and all 28 pin EPROMs except the 27512 varieties. It should be connected to Vcc (+5V) for the 2764, 27128 and 27256 type EPROMs. Pin 1 of the EPROM is the A15 address input for the 27512 EPROMs. This pin should be connected to ground when the 27512 EPROM is used.

The two threaded spacers are used to hold the EPROM socket circuit board securely to the 16 pin DIP header. The spacers should be fastened to the circuit (or perf) board using the two 4-40 screws (I used 4-40 button head SS cap screws, mainly for their small head size). The spacers are glued to the inside of the DIP header using epoxy glue. I used HEX spacers. I you use round ones, you will probably have to file a small bit off the sides of the header end of these spacers before they will fit inside the header. Allow the epoxy glue to harden thoroughly before proceeding.

The wiring can be completed with hookup wire. If you are using the circuit board, this can be done with straight pieces of bare solid wire, such as the leads from resistors, etc. If you are using "perf" board, you will need to use small hookup wire of approximately 20 to 30 AWG size. I found that 30 AWG solid "wire wrap" wire worked well for me. When using the circuit board, it is best to wire the circuit board up to the 16 pin header before you put the 28 pin EPROM socket onto the circuit board. This is because once you solder the socket onto the circuit board, the solder pads for the wires are hidden under the socket and become difficult to reach.

IMPORTANT: When you have finished construction be sure to double check your work. Make sure that the adapter is accurately wired and that there are no poor connections or shorted connections. Use your continuity tester to be certain that everything is hooked up correctly. Better yet, you can also test your completed adapter using your EPROM programmer as described below.

TESTING YOUR ADAPTER:

You can test much of the adapter wiring using your PROM/EPROM programmer. First program two banks of frequencies (32 channels) into an EPROM. It is best to use 32 different frequencies for this test. Then install the EPROM into the adapter and put the adapter into the programmer. Make sure than the bank switch wires (other than A8) to the adapter are connected to ground. Select the Signetics 82S131 PROM for the target device. Now use the programmer to verify that the data in the "PROM" matches the data that you programmed into the EPROM. If it does, you will have verified much of the adapter wiring, but not ALL of it. This test will check for proper wiring of most of the adapter, but does not test the bank switch wiring other than A8. You can easily test the bank switch wiring after you install the adapter into your radio, etc.

ACCESS TIME CONSIDERATIONS:

The Syntor® manual has no information about what kind of requirements the radio puts on the synthesizer PROM and I haven't found this information elsewhere. Access times for the PROMs used are about 70 nanoseconds maximum. Observation of the waveforms shows that the cycle time associated with reading the PROM is between 1.5 and 2.0 microseconds. This would seem to indicate that the longer access times associated with most EPROMs (100 to 500 nanoseconds) should not cause a problem. However, I have personally observed a case where one of my Syntor® radios would not operate correctly with a 28C64A EEPROM (150 nanosecond access time) that was properly programmed and installed in a properly wired adapter. I was able to correct this problem through a minor modification of the Syntor® radio. Power (+5V) is supplied to the Syntor® PROM through a switching circuit that turns power to the PROM "off" when it is not being read. This is done to minimize the current drain of the radio, particularly on receive. The current drain of the Syntor® PROMs amounts to about 100 mA. The specified access time for EPROMs (and PROMs) is usually measured from when the chip select line becomes active until when the data output becomes valid (with power applied to the device continuously). The access time can increase substantially if you measure it from when power is applied until the data output becomes valid. The modification that I made to correct this problem was to arrange for power to be applied to the PROM socket (and hence to the EPROM) continuously. Once this was done, I had no more trouble. The additional current drain of the radio was only barely apparent.

CONSTRUCTION DETAILS:

Some pictures of my first hand wired adapter:

Side view of the adapter. Note that the PROM socket is not centered under the EPROM socket. This is necessary so that the completed adapter will fit into the available space inside the Syntor® radio.

Top view of the completed adapter, with EEPROM in place.

Bottom view of the adapter.

Top view of the adapter. (Whoops! The two extra holes are a mistake).

Note: Syntor® is a registered trademark of Motorola, Inc.

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