RT85 Stuff:
We now have IRLP running on 70 cm (Station 634/635) thanks to some
RT85A radios we procured from The Royal District Nursing Service. Harry
- VK3BYY has spend considerable time and effort, not to mention money, converting
a batch of these radios for NERG members. Thanks go to Steve VK3TSW for
notifying us of their availablity.
The radios we obtained are actually designed for the 408MHz to
420 MHz band but may be tuned up to 430 MHz to 440MHz. There are other versions
of the RT85A's that work above 440 MHz, that could possibly be used, but
I don't have any experience with them. If you are looking for a UHF CB set,
they would be a better choice.
There are a couple of versions of the RT85A's with diffent microprocessor
control circuits. The original version of the radio used a 4 bit controller,
the HD44801 (I think) with a 2716 EPROM and shift register to serially
load the frequency synthesiser. Later versions have the processor replaced
with a 6805 mounted on a daughter board in place of the 2716 module.
The one of the 6805 versions uses a mask programmed MC6805G2 with
an outrigger 2716 for the channel and configuration data in the same
manner as the HD44810, the other uses a HD6305Y2P with 2764 containing
both the program and channel and configuration data. I have disassembled
the EPROMs for the Hitachi HD6305Y2P and hope to post the source soon when
i have cleaned it up. I used the EPROM from the RDNS radios, and
I'm not sure all the options are accessible in those EPROMs.
There is a BASIC program available for generating channel tables
however the option configuration bytes do not match the EPROM.
The channel table is suitable for the 2716 and also the 2764, but you have
to offset the channel table by 1000 Hex.
Receive channels are located from 1000 to 129F Hex, and the transmit
channels are located at 1400 to 169F Hex. The option configuration block
of the 2764 is located from 13F0 - 13FD Hex. I beleive the option bytes
are the same for the 2716. You have to do some manual editing of the eproms
to configure them.
The 2716s also have library routines at the top of the channel
tables that are loaded into the processors RAM. I am not sure what they
do, or whether they are needed for basic amateur versions of the radio
without Selcall. I have figured out most of the option bits for the 2764
from the disassembly listing, but can't be 100% sure I have it correct.
Drop me an email if you want the details or assembly code.
Links
An RT85 Users Group
has been set up on Yahoo. Its a great source of information on hardware
and software. Most of the links below can be found on this group.
Mark (Harry) VK3BYY
Has disassembled the mask programmed version (MC146805G2) of the RT85A
with the use of a printer port and some very clever library routines in the
2716 EPROM. He has also done a lot of work deciphering the RDNS code.
Brad Wooding VK3TAE
also has as a good page for RT85 firmeware information. I have taken his
70cm-vic-scan.bin file for the RT85C and disassembled it. It's available
below.
Mr Skinny
has links photos of the RT85 EPROM carrier as well as CB EPROM images.
Phil Rice VK3BHR
has information on low band RT85s.
Colb
has RT85 schematics scanned on his site.
My Data
