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.