IBM 6094-020 Lighted Program Function Keys
dkelvey at hotmail.com
Mon Jul 30 22:39:38 CDT 2007
>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
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.
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