Notes on channel programming for the Tait 495 B/1
-------------------------------------------------

The following was worked out from the chip data and by track tracing on
the rig. It works for me - but no guarantee given!

The synthesiser is an MC145152 with an MC12016 dual-modulus prescaler.

The reference is 10.24MHz, divided by 2048 in the synth, to give a channel
step of 5kHz.

The local oscillator on receive is 10.7MHz above the signal frequency.

The divider information for the synth is held on two 2716 EPROMs on a
plug-in daughter board. The EPROMs are soldered on the board, but if you
remove them, there is just about enough room to fit skeleton sockets so
that in future you can easily change the EPROMs. The clearance is very
marginal, so check your own rig before you fit the sockets. I found it
necessary to clip about 2mm off each EPROM pin to get them to sit lower
in the sockets, otherwise the daughter board wouldn't plug in properly.

On the 10 channel set only 20 bytes are used in each EPROM. The 10 bytes
starting at address 0 in each EPROM are used for receive frequency data,
the 10 bytes starting at address 100 hex are used for transmit frequency
data.

If you look at the daughter board from the component side, holding it so
that the edge-connectors make a letter 'T' then I will call the EPROM on
the left 'A' and that on the right 'B'.

When you run the T495 program, it will ask you for a frequency and then
give you two hex values for transmit and two for receive. The first value
in each pair goes in EPROM 'A' and the second in EPROM 'B'.

An example, say we want to set channel 3 to 29610kHz:-
Frequency (kHz): 29610
TX: 80 2C
RX: D0 96

Put 80 in byte 103h, EPROM 'A'.
Put 2C in byte 103h, EPROM 'B'.
Put D0 in byte 3, EPROM 'A'.
Put 96 in byte 3, EPROM 'B'.

To stop the program, press <Return> without inputting a frequency.

The 'C' source code is included, since it may well be possible to modify
it for other Tait rigs.

Good luck!


Roger Barker, G4IDE
June 1995
