Reverse engineering an AKD2001

 Per previous post, my unusal/1st gen AKD

 Some notes:

 

Processor: MC6802

PLL NJ88C30

EPROM 27C128 Mapped to $E000-$FFFF (mostly unused, No code before FC00, only 1K used)  

It seems to be a very simple design where the various 'peripheral' parts are memory mapped using a 74LS138 3-8 Decoder, it's not fully decoded so any write which addresses A13, A14, A15 or any combination will enable an output on the 'LS138


 

CP is the clock pulse for the 4024 Binary counter which generates the 1750 Toneburst 

CLK is the PLL Clock

Latch is the PLL Latch signal

FPSEL and FP14 are related to the front panel, not sure how that works yet

OE is the EPROM Select 

And some NOR logic:

 

'FP' signals are related to the front panel, the front panel connector:

 

Amazingly, the entire operating code for the radio takes only 336 bytes!

I don't think I could even persuade a modern processor to start up in that few bytes.

Memory map of EPROM: 

Reset Vector at $FFFE-$FFFF is $FC00 and yes, the code begins at $FC00

IRQ Vector is $FC71 and there's an IRQ handler routine there. 

IRQ seems to be from the front panel, suspect it's generated on keypress

Channel table seems to start at $FE00-$FFC7

The entire channel table:

0F 00 16 A8 15 14 1F 10 16 A9 15 15 2F 20 16 AA 15 16 3F 30 16 AB 15 17 4F 40 16 AC 15 18 5F 50 16 AD 15 19 6F 60 16 AE 15 1A 7F 70 16 AF 15 1B 00 80 16 B0 15 04 00 90 16 B1 15 05 00 01 16 B2 15 06 00 11 16 B3 15 07 00 21 16 B4 15 08 00 31 16 B5 15 09 00 41 16 B6 15 0A 00 51 16 B7 15 0B 00 61 16 B8 15 0C 00 71 16 B9 15 0D 00 81 16 BA 15 0E 00 91 16 BB 15 0F 00 02 16 BC 15 10 00 12 16 BD 15 11 00 22 16 BE 15 12 00 32 16 BF 15 13 00 42 16 94 14 E8 00 52 16 95 14 E9 00 62 16 96 14 EA 00 72 16 97 14 EB 00 82 16 98 14 EC 00 92 16 99 14 ED 00 03 16 9A 14 EE 00 13 16 9B 14 EF 00 23 16 9C 14 F0 00 33 16 9D 14 F1 00 43 16 9E 14 F2 00 53 16 9F 14 F3 00 63 16 A0 14 F4 00 73 16 A1 14 F5 00 83 16 A2 14 F6 00 93 16 A3 14 F7 00 04 16 A4 14 F8 00 14 16 A5 14 F9 00 24 16 A6 14 FA 00 34 16 A7 14 FB 00 44 16 C8 15 1C 00 54 16 C9 15 1D 00 64 16 CA 15 1E 00 74 16 CB 15 1F 00 84 16 CC 15 20 00 94 16 CD 15 21 00 05 16 CE 15 22 00 15 16 CF 15 23 00 06 16 A8 14 FC 00 16 16 A9 14 FD 00 26 16 AA 14 FE 00 36 16 AB 14 FF 00 46 16 AC 15 00 00 56 16 AD 15 01 00 66 16 AE 15 02 00 76 16 AF 15 03 00 07 16 C0 15 14 00 17 16 C1 15 15 00 27 16 C2 15 16 00 37 16 C3 15 17 00 47 16 C4 15 18 00 57 16 C5 15 19 00 67 16 C6 15 1A 00 77 16 C7 15 1B 00 09 16 C0 14 FC 00 19 16 C1 14 FD 00 29 16 C2 14 FE 00 39 16 C3 14 FF 00 49 16 C4 15 00 00 59 16 C5 15 01 00 69 16 C6 15 02 00 79 16 C7 15 03 

 

Each channel seems to be 6 bytes of data, 

First channel:

0F 00 16 A8 15 14

16 A8 is the TX VCO divisor

15 14 is the RX VCO divisor 

Our Reference frequency is 25KHz

In this case, $16 $A8 equals 5800 Decimal, 

5800 * .025 = 145MHz

RX Divisor $15 $14 = 5396

Same as before, 5396 * .025 = 134.9MHz 

RX Frequency = RX VCO + 10.7MHz IF = 145.6 

So the first channel is set up as a repeater, 

The 4024 chip in the radio seems to be a 1750Hz Toneburst generator, pretty useless these days but it must be switched on or off, not sure if it's in the EPROM or not, yet.

There will also be information for the 7 segment LED display, I suspect it's the $0F $00 but haven't reverse engineered the front panel yet.

 

 More later.

Location: Greater Manchester, UK

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