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CFA835 xmits '0xc0' on startup?


New member
Hi all,

Been watching the CFA835's output on a cold start. It seems to issue a 0xc0 byte just after DC power is applied, i.e., upon cold start (my design alows me power up/down the display via software control)

Is this byte deliberate, and can it be relied upon to signify the display's serial stack is ready business?
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Last edited:

CF Mark

I gather this is on the serial output, not USB?

I will say now though that it is not deliberate, so do not rely on it.
Sending a ping packet is the best way to check for presence.


New member
Yes, this is on the serial port. And I mis-reported: it is '0xc0' (not 0x0c).

It seems 100% reliable. The problem I see with 'pinging' is that it is something I have to spend cycles doing. A simple packet sent when CFA835 is available would be helpful.

Is it possible to check with the developers to see if this is deliberately in the code, and 'undocumented' feature, perhaps?

(On another note, can you fix the thread topic? I can't seem to be able to fix the error)

CF Mark

I've done some testing here, and am yet to see the 0xC0 byte (or any other) appearing on the serial port when the CFA835 is powered on.
Can you please tell me the firmware version of your CFA835? The easiest way to read the version number is to hold the right key while powering on the module.
Have you changed the default interface settings (usb or serial port options) using command 33 (0x21)?
Is the 0xC0 byte sent after using the "CFA835 Restart" command (cmd:5 data:8,25,48)?

I am the developer of the CFA835's firmware.
As i said above, the CFA835 should not transmit any data on the serial interface after power-on or reset.
I will discuss sending a packet to notify of power-on with my colleagues.
USB LCD Displays - Graphic and Character LCDs with a Keypad
Perhaps this 0xC0 is a startup transient being misinterpreted due to a baud rate mismatch. How is the serial port setup regarding normal/inverted levels, or ttl/rs232 levels?