IBM 6094-020 Lighted Program Function Keys

dwight elvey dkelvey at
Mon Jul 30 22:39:38 CDT 2007

>From: "Michael B. Brutman" <mbbrutman-cctalk at>
>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.


More information about the cctech mailing list