EPROM PROGRAMMING for the WEPIX-2000-B RECEIVER


Step-by-step calculations using a programmer's calculator. This is a scientific calculator that does decimal and binary arithmetic and automatic conversions from one radix to another (ie: displays 137.000 as 89 or 10001001). Note that only integers can be converted. If you don't have a calculator like the one described above you can download one from http://www.shareware.com

It's usually best to do the calculations in the order you wish to scan the frequencies starting from the first frequency at EPROM address 0000. The frequencies can be in any order you like but the order can't be changed once you've burned them in except by erasing the EPROM and starting over. Each frequency will use 8 bytes of EPROM. The NJ8820 allocates a fixed number of bits for each of its 3 counters. The calculations will be done for one counter at a time. Calculations that do not fill the entire counter must be filled in with zero's.

1. SWITCH to DECIMAL mode (called "floating point" on some calculators)

2. ENTER FREQ. IN MHZ (137.795)

3. SUBSTRACT I.F. 10.7 MHz. (137.795-10.7=127.095)

4. DIVIDE BY .4 if in 10 KHZ steps or .2 if in 5 KHz steps. This is a short cut derived from calculations involving the prescaler divide ratio and channel spacing). Since the entered frequency in this case ends in 5 KHz you must divide by .2 (127.095/.2=635.475)

5. STORE that number (635.475) in calculator memory for later use.

6. ENTER integer of that number (635)

7. SWITCH calculator radix to HEX. Displays 27B

8. SHIFT LEFT 2 places (this is necessary because the 8820 ignores the first two bits of the first 4 bit byte. Displays 9EC

NOTE: you can observe the left shift on your calculator by switching the radix to BINARY (called radix 2 or base 2 on some calculators) but you'll have to shift back to HEX (radix 16) to record the results.

9. On a sheet of paper record the first 3 bytes of the binary file you will use to burn-in the EPROM. Note that since the EPROM uses 8 bit words whereas the NJ8820 uses 4 bit words, the left hand nybble of each byte must be zero (actually it can be anything since it's not read but using zero will avoid confusion) Also note that binary files are usually entered in reverse order. 9EC thus becomes OC 0E 09.

10. Switch to decimal mode. RECALL memory. (635.475)

11. ENTER fraction only. (.475)

12. MULTIPLY by 40 (from prescaler divide ratio ). Displays 19.

13. SWITCH to HEX. Displays 13. (no left shift this time)

14. On paper enter the next 2 bytes. 03 01.

15. So far we've programmed 2 counters in the NJ8820 and recorded on paper the following: 0C 0E 09 03 01. We have 3 more bytes left for the crystal reference divider. This need only be calculated once since it remains the same for each output frequency UNLESS you change the I.F. (10.7 MHz.) or the channel spacing (5 KHz).


TURN THE PAGE

16. Switch to DECIMAL. Enter reference crystal frequency (4.0 MHz.) divide by channel spacing, in this case 5 KHz or to keep everything in MHz (.005). 4.0/.005 = 800. Since the NJ8820 has a fixed internal divide-by-2 in the crystal reference divider you must divide 800 by 2. This gives 400.

17. Switch to HEX. Reads 190. Transpose and add left hand zero. Reads 00 09 01. This will remain the same for all frequencies but it must nevertheless be repeated in the EPROM since it reads a new address for each frequency.

18. The complete sequence for 137.795 MHz is : 0C 0E 09 03 01 00 09 01

The EPROMs supplied starting Nov. 6, 1990 have been programmed as follows:
Frequencies are in decimal. Addresses and data are in hexadecimal notation.
The oscillator frequency is the signal frequency minus the intermediate frequency of 10.7 MHz.

Sig. Freq. Osc. Freq. Address Data

137.035 - 126.335 - 0000 - 0C 0D 09 0B 01 00 09 01
137.280 - 126.580 - 0008 - 00 0F 04 02 01 08 0C 00
137.300 - 126.600 - 0010 - 00 0F 04 04 01 08 0C 00
137.400 - 126.700 - 0018 - 00 0F 04 0E 01 08 0C 00
137.500 - 126.800 - 0020 - 04 0F 04 00 00 08 0C 00
137.620 - 126.920 - 0028 - 04 0F 04 0C 00 08 0C 00
137.795 - 127.095 - 0030 - 0C 0E 09 03 01 00 09 01
137.850 - 127.150 - 0038 - 04 0F 04 03 02 08 0C 00

BANK 2

137.485 - 126.785 - 0040 - 04 0E 09 05 02 00 09 01
137.490 - 126.790 - 0048 - 04 0E 09 06 02 00 09 01
137.495 - 126.795 - 0050 - 04 0E 09 07 02 00 09 01
137.500 - 126.800 - 0058 - 08 0E 09 00 00 00 09 01
137.505 - 126.805 - 0060 - 08 0E 09 01 00 00 09 01
137.510 - 126.810 - 0068 - 08 0E 09 02 00 00 09 01
137.515 - 126.815 - 0070 - 08 0E 09 03 00 00 09 01
137.520 - 126.820 - 0078 - 08 0E 09 04 00 00 09 01


The frequency and address columns are not part of the binary file. Enter only the data portion and do not skip a line between bank 1 and 2. Follow the instructions for your particular EPROM programmer.

If you don't have an EPROM programmer you can get one for $159 (Cat. #ACP-10000) from Personal Computing Tools at 1-800-767-8728. They sell with a 90 day trial, money back guarantee. Another good source is JDR Microdevices, They have one for $129 (cat. #MOD-EPROM) but check the features. Both will work with our 2716 EPROMS but may have different features that might be useful to you for other projects.

Note that in bank 1 we've calculated on the basis of 10 KHz channel spacing except for 137.035 and 137.795 which must be calculated using 5 KHz. We could have calculated all the frequencies on the basis of 5 KHz as was done in bank 2 but we like to use a high reference frequency as possible since the reference frequency also becomes the sampling frequency and 10000 samples per second are better than 5000 samples per second. This reasoning shouldn't be carried too far however since other factors come into play. For all practical purposes we have found no difference in the performance whether using 5 KHz or 10 KHz channel spacing.