Hi, I have a Mensch 265QBX microcomputer, and unable to connect to it over serial.

http://wdc65xx.com/mensch-w65c265qbx-getting-started/#

I bought the recommended TTL to USB interface from SparkFun, and I'm pretty confident that the serial module is working (it echos characters back to my terminal with a TX/RX loopback). The serial board is happily providing the 265QBX with 3.3v, as far as I can tell.

Upon power-up, ALL LEDs light (four red, four green), then after about 20 seconds the RX LED (on the serial board) starts flashing for about 20-30 seconds, like the board is loading something. But I never get a ROM monitor.

It seems the default settings are 9600/8/N/1, but I can't get anything out of the board. I've also tried swapping the TX/RX pins. I have nothing else connected to the board. On some terminal programs, I get a string of periods. (I've tried Minicom, CoolTerm and GNU screen).

Am I missing something obvious here? Bad board? The documentation and help for this thing is pretty sparse...

Thanks.

Hi Hartze11 - welcome

I do not have that tiny board but the SXB board containing the same MPU. It is powered through USB - so to say the Spark Fun is "integrated". Catching the first greeting string is difficult, because my terminal program won't start using the serial port simply because the port isn't present unless the board is attached ...

So you may use the reset button to look whether something changes. Your settings (9600/N/8/1) is correct. Your terminal settings should disable the use of RTS(P57, J5.6) / CTS(P56, J5.2) ("Flow control = none") but your interface should be connected to these signals as well as to RxD(P66, J5.4) / TxD(P67, J5.5). If without flow control still nothing appears, try RTS/CTS handshake as well.

You may also check PHI2 (J2p4). It should start with 32,768 KHz (briefly) then switching to 3,6864 MHz. If this won't appear the crystal may be poor or broken. You could try to get it running with a wet finger across the pins of the 3,6MHz crystal - this way you add a parallel "resistor" which helps the oscillator to get running.

You could check the Reset signal at the button. One side should show Vcc the other GND. Pressing the button should lower Vcc to GND.

Good luck !


edit(1): what I remember when trying crystals with higher frequencies: each time the Reset button was hit, the high speed oscillator was turned off then on again - but if the crystal frequency was not 3,6864 MHz the terminal settings didn't work although the default setting of the Mensch monitor is 9600/8/N/1 for 3,6864 MHz. So I was forced to start with 3,6864 then pull out and replace the crystal and sometimes gave it a little kick (wet finger).

The 32 KHz oscillator is always running. But it is a bit difficult to check - on pin 37 of the MPU. Because the MPU starts with this slow clock, nothing would happen if this clock is not running.

Does this fall within the "lift your Apple /// 4" off the desk and drop it" family of diagnostics?

no its a simple way to give a crystal oscillator a little kick if it won't run otherwise

It's to bias the input.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Hmmm, if the board is transmitting its greeting message using a totally wrong adjusted baudrate, you would notice the same.

During startup the µC checks whether there is external ROM with a "WDC" (or WDM ?) signature. If so, it would leaving the monitor. If not, it starts FCLK (3,6864 MHz) wait for stabilization, switch to FCLK, then wait for one timer T1 (CLK (32 KHz) driven) to wrap around, and then try to determine the FCLK frequency. After that the UART is initialized and the greeting message is transmitted.

Now, if the FCLK (3,6864 MHz) is ok, but CLK not, just receiving some noise, hum, etc. this long delay could be possible as well as the wrong baudrate.