Expand the radio to 16 channels, Alternate Method
A much slower but just as effective way of doing it is to use Hex Workshop to edit the saved file. The saved file from the GP300/P110 uses some form of encryption that changes the look of the file each time it is saved in RSS. This can sometimes make the below process long and boring.
First, make a backup of the codeplug file you want to edit (copy it to a .bak or something). In the event you loose track of which bit you are editing and get a Error 58, its easy to start over again.
Next, load your codeplug file into your hex editor. You want to edit the byte right after the end of the serial number. Make a note of it's original value and increment it or decrement it by one and save the file.
Exit the hex editor and start up the GP300 RSS. Try loading the file you just edited, you will either get an Error 21 (Radio not supported) or the codeplug will load okay (once in a while you may get an Error 58, but this isn't very common).
Note the model number that the codeplug has loaded as, and compare it to the original model number of the radio. If the nineth character of the model number is a "C" (ie. P93YPC20C1__) you have a 16 channel codeplug. Also, make sure that the rest of the model number is the same, otherwise you may have made a 16 channel codeplug on some other band!
If the RSS won't load the codeplug, go back to the hex editor and change the bit again, save the file in the hex editor and try loading it again. Keep repeating this until a) you get tired and give up, b) you are successfull, or c) you edit that byte all 255 times. If you have come to point c), edit the byte to something you know that works, load it in RSS and re-save it in RSS. This will re-encrypt the file and you can continue editing.
If you want to do this faster, you should check out the Hoffis pages (above) and disable the encryption for the codeplug. Heck, if you can manage to do that, you should be able to make the 16 channel modification easily then. :)
Tips:
run the RSS in one DOS window of Windows 3.1x and the hex editor in another to make swapping between the programs less painfull
try editing the byte up and down a ways and see how many "good" loads you get, you will probably find that the "good" loads will be somewhat grouped together
if you aren't having much success finding many combinations which will load, re-save a good codeplug in RSS to scramble the codeplug and keep trying.
Note: Sometime in 1994 Motorola changed the 2 channel radios such that if you were to hack the radio into an 8 channel model, you still get 2 channels. The change was the microprocessor to a new unit that only recognizes the common and 1 line of the channel selector. The channel switch is the same regardless of which radio you have. Only by changing the CPU can you then change the number of channels to more than 2. To tell if you can convert your radio, pop the knob off and turn the selector. If the 2 channels programmed in the radio come up in the order 1,2,2,2,2,2... it will work. If they come up 1,2,1,2,1,2,1,2... forget it, you'd probably have to change the microprocessor to get it to work.
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Expand the radio to 16 channels, Alternate Method 2
Depending on which firmware is in your radio, this may or may not work (see Note above).
Open the GP300.MDF in your Hex editor and make a Checksum-16 of the whole file. You will need this later, so write it down. For RSS version 5.00 I got a checksum of 0xF2D3.
Search for your model number in the file, you probably will come accross more than one entry so you can either change them all or change them one by one until it works.
Once you find your model entry you should see something like this:
0000086C 50 39 34 59 50 43 32 30 43 33 5F 5F 06 1F 10 04 27 40 14 20 19 50 P94YPC20C3__....'@..P
If you look at this model entry, the third byte after the model number (offset 0x87A) is a 10. This is the hex representation for the number of channels in the radio, in this case 16ch. Most of the time you will see a 0x02 or 0x08 in this position for 2 or 8 channel radios respectively. Try changing the field to 0x10 to make a 16 channel radio and see what happens. Also note the 06 at offset 0x878, this is the bandsplit for this model number and corresponds with the bandsplit entry in the table at the top of the .mdf file.
The .mdf file for these radios is checksum protected and every time the RSS loads it calculates the checksum for the file and compares it to an internal reference to see if it matches. If the checksums do not match you will get an error message.
The only way we have to correct the checksum of the file at this time is to keep editing bits and making Checksum-16 calculations until the edited file's checksum and the original match. You can either edit the Copyright statement or some of the model descriptions in the file. Just take one or a few of these insignificant bytes (some experimentation may be required depending on by how much the cheksum is out) and add or subtract a few bits of the numbers make a Checksum-16 of the file. You should notice the checksum has changed by the number of bits you added or subtracted. Keep going until the checksum's match.
To find out if you picked the correct model number to edit, save the .mdf file and load your radio's codeplug into the RSS. Try adding channels with the Mode Utility and see what happens.
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Some other RSS modification tips for the GP300
GP300 RSS ver.R07.00.00 31-Oct-94.
If you would like to program any GP300 radio with the codeplug information previously got from another GP300 (serial number, model, freq. range etc. doesn't matter), do the following:
In the file gp_2.ovl. look for signature C6 46 FC 00 9A E3 08 at offset 10949 (2AC5h) and modify three bytes from ** into 90h:
Old string = C6-46-FC-00-9A-E3-08-XX-XX-**-**-**
New one = C6-46-FC-00-9A-E3-08-XX-XX-90-90-90
XX means the value doesn't matter, leave old values (these bytes contain segment address and may vary).
Run gp300.exe and load archive file with the codeplug info previously saved on disc.
Press (F8) and program any target GP300. Model number, serial and features will be copied into it.
If you want to disable frequency checking for entering out of band frequencies in RSS, try doing the following modifications:
Search for 77 10 around location 3E80 and replace with 90 90
Search for 77 03 around location 3E8D and replace with 90 90
One disables frequency checking on tx, the other on rx. Note that the locations will vary depending on the version of RSS.
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