Mark wrote:
> I have a circuit that uses an old mylar type pad for input of numbers 
> and letters. The problem is the pad is beyond repair.
> So I opened the device and found  that it is controlled by a TMP47C443 a 
> 4bit micro made by toshiba.
>
> The pad has about 16 keys, but a sample of how they connect is below:
>
> 1 - pins R80 + R62
> 2 - pins R81 + R62
> 3 - pins R82 + R62
> 4 - pins R80 + R61
> 5-  pins R81 + R61
> 6 - pins R82 + R61
>
> R80 - R82 are listed as:
> 4 bit I/O port with latch.
> When used as input port, external interrupt input pin, the latch must be 
> set to 1.
>
> R62-R62 are listed as:
> 4 bit I/O port with latch.
> Every bit data is possible to be set, cleared and tested by the bit 
> manipulation instruction.
>
> The circuit interfacing the TMP47C443 chip to the keypad is pins R80-R82 
> each pass through  a signal diode with the anode side connected to keys.
> The R62-R62 pins connect directly to the keypad but have a 10K resistor 
> tied to +5v.
>
> What I really want to do is connect a pic to this circuit so that when 
> the pic pulls a pin(s) High or Low the corresponding key is entered on 
> the device.
> The device uses a total of 10 pins to connect to its keypad and I have 
> several pics with more than enough pins .I have already tried pulling
>   the various pins high and low on the device but unless I connect the 
> exact pins like a switch it will not register as a keypress.
>   I wanted to do this with just a pic and not use additional parts .  
> Can someone point me to how this other micro is interfacing the keypad
>   so I can emulate it with a pic.
>   
It sounds like you have a multiplexed matrix keypad, Most likely one 
side of the matrix (almost certainly the side without the pullup 
resistors) will be controlled by output signals from the micrcontroller 
and scanned by pulling one output low at a time to activate groups 
(usually rows or columns) of keys.  The lines on the other side of the 
matrix are then used to read to read the state of the current group.

A pic should be able to follow the old micros outputs and output the 
signals for the relavent row of keys. The only possible issue I can see 
is that depending on how quickly the microcontroller reads a group after 
activating it the pic may need to respond very quickly.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist