From: "Michael B. Brutman"
<mbbrutman-cctalk at brutman.com>
I'm still trying to make this thing talk ...
Here's the quick recap. It is driven by a derivative of an Intel MCS-51.
It is supposed to speak 9600 N81 over a serial port to a PC. The protocol
is supposed to be simple. But I haven't been able to make it talk.
I borrowed a friend's multi-meter that does frequency counting, hoping to
use it as a poor man's oscilloscope. I verified it with the PC serial port
- sending characters definitely makes it wiggle.
Connected to the device (which is powered by an external adapter), it shows
+10VDC on its pin 2 (which is 'receive' from the PC perspective), but no
wiggling with the frequency counter. This confirms what I saw with my
meter - a straight 10VDC signal coming out. The voltage level is fine for
serial, but it is not a data stream if it is continuous.
Opening the device up shows the MCS 51 feeds a Maxim chip, which is used to
get the TTL voltages up to proper RS232 voltages. The input and output to
the Maxim chip are behaving the same way - a continuous voltage. Kind of
like the MCS 51 is fried or stuck in a loop waiting for initialization.
(And of course, I don't know what it expects.)
The unit has a small switch on the backside that is either in a 'normal' or
'loopback' state. It appears to function in loopback - you can press a
button and the light for the button turns on, turning off any other
previously lit button. But nothing comes out of the serial port in that
state. In normal state it does absolutely nothing, and has the steady
voltage on the output pin.
Is it possible thing thing is waiting for the serial port to set one of the
other pins for flow control? Any other ideas? (I need an oscilloscope
...)
Regards,
Mike
Hi
First try removing the Maxim chip. It may be shorted. Next,
send a copy of the code you are using to control and what
frequncy the processor is running at. If the crystal isn't 12 MHz
( as I recall ) the baud rate may be differnt.
Dwight
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