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Embedded Systems, Publishers

DonTronics - DT102


dt102c.GIF (27488 bytes) dt102cd.GIF (24344 bytes)

The DonTronics DT102 PCB has been designed on a 2.5" SimmStick platform, and is same size as the DT205 Relay board.

It has provision for six "Hat Key" type push button switches, and a standard 2 by 16 LCD. The board is designed for the Truly brand LCD, however many others will fit the standard 16 pin header strip provided. Mounting holes are provided for the Truly display which mounts via female/male header pins on the component side of the board, and above components such as the PIC16F84 micro. Yes, the micro will fit in a socket if need be, right under the display. The display is very simply removed.

Two RJ-45 connectors allow RS-485 communications via an 8 wire standard cables. Two jacks means RS-485 can be used on multiple connections or drops. These RJ-45 PCB mount jacks need to be mounted on the solder side of the board.

Also on the solder side of the board, you will find a spot to mount a 5 pin DIN PCB connector, same as the one in your standard PC. This allows an "AT" type keyboard to be plugged in as an alternative to the 6 push button switches.

Other features:
Max-232 and single wire comms will be catered for to some degree. Details to be available in the future.
Configuration jumpers for various programmed feature selections.
On board Piezo buzzer
PIC16F84 4Mhz crystal or resonator operation. (PIC16C61 and others can be used)
LCD contrast control.
Powered from RS-485 bus or SimmBus.
Power ON LED
Debugger LED and link. (RS-485)
Termination resistor and link. (RS-485)
On board +5V regulator and support circuitry.

dt102aov.gif (39365 bytes) truly216.jpg (10756 bytes)

Special notes regarding the circuitry used.
The keypad matrix uses a technique described on the microchip website.

Configuration jumpers ( J4 ) use another multiplexing technique. Essentially when the PIC needs to read the configuration jumpers the i/o port is configured to be an input and the 'E' ( RA2 ) pin is configured to be an output with a logic low. The configuration information is then obtained by reading the appropriate input ports. The resistor pack bias resistors ( RP1 ) for the configuration jumpers are needed to prevent any interaction between the normal functions of the i/o lines and the configuration jumpers.

In 'normal' operation ( when not reading the configuration jumpers )  either the PIC or the LCD would be driving the i/o lines. The bias resistors common line is connected to the 'E' ( RA2 ) line to make sure that the correct
voltage levels are present on the i/o lines during all phases of operation.

Serial communications.
There are three possible hardware interfaces for the serial communications to and from the DT102.

  1. RS232
    This uses the conventional MAX232 interface chip to provide the appropriate voltage level / conversions. The protocol used is full duplex.
  2. RS485
    This uses a LTC485 driver chip to provide the differential drivers and receivers required for RS485. As RS485 is a simplex interface we use RA3 to control the LTC485 driver chip to be in either receive or transmit mode. Because it is only simplex we also multiplex the rx/tx data into the PIC onto RA4. The RS485 interface uses RJ45 connectors to allow multiple devices to be connected to a common serial bus. The RJ45 interface also has power and ground available. By using a serial protocol that has an unique 'identity' each device on the bus can be individually addressed.
  3. Logic interface.
    This interface uses the open collector capabilities of the RA4 on the PIC chip. The protocol is also simplex but allows for limited distance communications while only consuming one i/o pin on the PIC. the protocols used are the same as in the RS485 interface.

At the time of writing, software isn't available to make use of the "AT" keyboard input, however code can be found at Steve Lawther's site at: This may need to be re-configured to suit the DT102 board. Code can also be found at Mauricio Culibrk's site at:
Steve Lawther's "AT Keyboard/LCD" Schematic

Other Software will be available and full details will be announced in the near future;
Here are some of the specifications:

LCD software specs.

Firmware for the DT102

Available as a preprogrammed PIC processor.

Functionally similar to Peter Andersons and/or Ben Wirz exceptions are the baud rate is limited to two different rates, only one type of display is supported ( should be able to cope with 16, 20 or 40*2 ).

Baud rates either 2400 or 9600, jumper selectable.  ( jumper A on = 2400, jumper A off = 9600 ), data format 8 bit no parity and one stop bit.
6 way keypad can be polled by sending the following string. FE F0 ( in hex ) to the DT102, the DT102 will respond with the key status as a single byte. Any key that is still active or has been active since the last poll will be or'ed together to avoid missing any key presses.
Self test mode ( pressing key 1 during reset enters test mode )

Test software for the DT102

Test software for the DT102 to operate with the DT102 firmware ( 1.4M ). Download into a temporary directory, unzip the file, then run the setup program.


Circuit diagram for DT102

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Last modified: February 24, 2024