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Hi everybody,

I'm trying to connect a bluetooth module to a 6551 ACIA, but maybe I think, that it's too simple

I am using a HC-05 bluetooth module, that should be able to connect to a UART TTL source, but it does not seem to work. I tried to connect Rx to Tx and vice versa. Has anybody tried something similar? Maybe, I need some level shifters? The ACIA seems to have a 5V TTL output, is that correct?

Cheers,
Michael

Hi Michael,

Can you post the part # of the bluetooth module?

Daryl

Hi Daryl,

I have the same module, as seen here:

http://www.instructables.com/id/AT-comm ... th-module/

So, it's not only the module, but it's on a breakout board. I tried to configure the module with AT-commands with an USB-TTL adaptor. This works.

Cheers,
Michael

The HC-05 is a strict 3.3 V device, so be careful with TTL 5 V power and signals. Power with 3.3V and lower the TX with a voltage divider.

http://www.tec.reutlingen-university.de ... -Modul.pdf was helpful for me in the past.

Check if you did not switch TX and Rx connections, and there is the KEY/EN input to think about. And baudrate.

I believe the 6551 needs an external CTS signal to enable its transmitter. Have you connected it to something?

Thanks for your answers!

I connected only Rx and Tx, nothing else. Should I connect the RTS/CTS lines, too? They seem to be on the module on Pin 3 and 4. I assume, that they are 3.3V level, too.
Is a voltage divider okay, or should I use some IC for that?

The key pin is needed for AT command, I've already configured the module. But for that, it was connected to an USB-TTL adaptor and not to the ACIA.

Cheers,
Michael

I'd wire the 6551's CTSB pin to its own RTSB.

Here are few ideas to built on top of the others already presented. I'll assume your breakout board provides the 3.3v to 5v conversions - if not, you need to address that too.

You proved the BT module with the USB-TTL adapter and you said you configured it. Does it retain things like baud rate settings through power down/power up cycles? What baud rate is the BT module using?

Next, on the 6551, connect it to the same USB-TTL adapter and ensure it is transmitting and receiving and at the same baud rate as the BT module.

If both of those steps can be repeated individually, even through power cycles, then my guess is they will work when you connect the TX-RX, RX-TX, and Gnd-Gnd.

Daryl

Okay, I've tested the USB-TTL adaptor. I have now a level converter between the ACIA and the USB adaptor. There is still no communication. The USB adaptor has RTS and CTS lines, should I try to connect them to the ACIA, too?

The bluetooth module stores all settings, I make.

Sounds like your 6551 is not functioning properly yet. Can you verify the crystal connected to pin 6 & 7 is functioning? Also, connect the cts, dcd, and dsr pins to gnd. Now connect just the USB tx, rx, and gnd to the 6551.

it would help if you would provide the code you are using to configure the 6551 and give us an idea of how you can verify it is functioning (i.e., is your system running a system monitor that accepts commands and returns data via the 6551?)

Daryl

One other inquiry.... which (brand, lot#, etc.) 6551 chip are you using??

I was able to get my Rockwell R65C51 to connect using an HC-05 with no trouble. I did add a voltage divider to the RXD line to drop the 5v down to ~3.3v to play it safe, but it did work at the full 5v when I did a quick test. I'm still trying to get an HM-10 (V4.0 BLE vs. V2.0) to work, but it hasn't been cooperative as of yet.