Reading Game Cartridge (Atari Lynx II)
The Atari Lynx II reads the game data from the cartridge in bursts, storing the game in RAM until further loading is needed. Once it is loaded, the cartridge does nothing and there is no activity on the cartridge pins.
The basic setup during game load is:
- Suzy and Hayato talk to each other to establish they are ok
- Suzy then pulses the CART (!CE0) pin to read the first 4 bits of data from the cartridge ROM
- If Suzy is bad, or sometimes the RAM, A1/2/3 would pulse at boot then stop
- Once the header is read and confirmed ok, SWCOM (!CE1) is pulsed also and all data is read to load the game
If the U7, U8, Suzy, RAM or any pins between them are faulty the address will only clock up a little then everything will stop.
If you get no activity at all on the address pins on boot, then the Suzy or Hayato is faulty, or shorts/broken traces between them, as the Suzy and Hayato have to initially talk to each other before Suzy starts the game load.
For probing for activity and initial game load, due to the above, you are best probing the desired pins right as you apply power.
If you bridge pins 31 and 33 on the cartridge slot to prevent the Lynx knowing the game is inserted or not, you can turn the console on with the game inserted, then once loaded remove the game and have it still play.
On boot the Suzy drives pin 32 (SWCOM, !CE1) and pin 35 (CART, !CE0) low in pulses as it needs to read in data.
These pulses go through diodes D3 and D4 into the hex inverter U7 pin 3 (schematic says pin 5 which is wrong) then out on pin 4 inverted. Pin 3 also goes to the ROM cartridge pin 27.
When either pin is low, the output to the clock of U8 pin 10 (a counter) is high, causing it to clock in and increment the ROM address pins 0 to 10.
At the same time the pin 12 (ROM/TAPE) of the Hayato chip drives the input B pin 2 into the U9 (serial-in parallel-out) chip to se the address, which shifts ROM addresses 12 to 19 every 8 pulses of the pin 9 (MOTORON) which goes to the Clock of U9 and Reset of U8 (resetting address 0 to 10 to low).
In short, the pulses on pin 32 (SWCOM) and pin 35 (CART) from the Suzy chip increment the lower ROM address to be read from the cartridge and the Hayato increments the higher ROM addresses using pin 12 (ROM/TAPE) and sets the data for those registers using pin 9 (MOTORON).
The data out of the ROM cartridge is then passed into the Suzy chip for processing.
To check the Hayato and Suzy are operating correctly it is best to check without a game inserted.
Without a game inserted, power on the system and monitor pin 9 (MOTORON) from the Hayato chip. This should pulse high 8 times and then idle for around 2 milliseconds before repeating over and over indefinitely.
This is the U8 counter Reset pin being driven 8 times to read out the first byte of data (the game header, D0/1/2/3/4/5/6/7 as a byte). It repeats this 8 times and if the first byte fails to provide any data of use those 8 times in a row, it pauses for 2ms then repeats forever.
The pin 12 (ROM/TAPE) which sets the higher address bits will never toggle as it fails to load the lower address bits.
On the Suzy chip, pin 35 (CART) will pulse low once every 2 milliseconds which drives the clock of the U8 counter to increment the address once from byte 0 to byte 1.
The Suzy pin 32 (SWCOM) will remain high at all times as it will never progress past the first byte of failed load.
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