This page will describe the basic operation of your 912B32 board, and how the boards configuration options can be used.

Basic Operation

Once you have assembled your board, you need to know how to connect power, then set it up for programming. The MC68HC912B32 part comes from the factory completely blank. Therefore, you must program it before it can do anything.

To program this part, you will need a BDM12 interface pod,  or an equivalent board from another manufacturer. My instructions are going to assume you are using a BDM12 interface pod.

Setup for Programming and Debugging

Here is a list of things to do in setting up the board for programming.

1. Connect a 5 volt power supply to the POWER pins
2. Connect a well REGULATED +12v power supply to VPROG
3. Connect a BDM12 to the BDM12 port. Be sure you understand where pin 1 is on the cable and on the board.
4. Slide SW1 into the PROG position.
5. Using your BDM12 download software, issue a reset command, then use the fload command to download your .S19 file.
6. Once the programming is done, you can set SW1 to the Run position.
7. If needed, you can run your debugger software to single step and otherwise debug your code.

These steps should get you setup to program your board.

Normal Operation

For normal operation, it is recommended that you do the following:

1. Place SW1 into the RUN position. This disables the VPROG voltage from reaching the part.
2. Connect +5 volts to POWER

On powerup, the chip will enter normal single chip operation mode, and execute whatever software you have previously loaded.

Optional changes to the board

I have configured this board to run just fine in stand alone mode. I have also added a few options via cut jumpers in the event that you wish to change the configuration on the board. The following describe what each of the cut jumpers on the board do. I have organized them according to functionality.

The cut jumpers are made up of three surface mount pads. To cut a jumper, you need to remove the pad that connects the outer two pads. This creates a break in the surface. You can now use the outer pads to solder on a jumper wire to connect the circuit to some other connection point.

A/D Conversion Voltages

The A/D converter comes default using Vdd and Vss as the reference voltages. If you would like to connect your own reference voltages, you will need to cut jumpers JP4 and/or JP5 on the top of the board. JP5 is connected to the Vrh pin and to Vdd. If you cut JP5, you can replace Vrh with your own signal by either soldering a jumper to the appropriate pad on JP5, or connecting to pin 49 of the CPU. Likewise, JP4 is connected to pin 50 which is Vrl.

The A/D converter also comes default with VSSA and VDDA connected to Vss and Vdd respectively. If you wish to change this default behaviour, you will need to cut JP6 and JP7

RS232/TTL Conversion

One of the larger optional sections is the RS232/TTL conversion section. This section uses a MAX3221CAE part, which is a low power converter. The nice thing about this converter is it uses extremely little power in its shutdown state (approximately 5 uA). Thus, if you wish, you can install the part and practically ignore it. Otherwise, you can leave off IC4, C4, C5, C6, C7, and C8 and the board will function without it.

The MAX3221 part will stay in shutdown until it finds a valid signal on the RX line of the SERIAL0 connector. When this happens, the part will resume operation by starting the charge pump. If you wish, there is an additional connection that isn't implemented on this part called the INVALID/ pin. I have brought this connection out to an unmarked pad on the bottom side of the board. It is called the INVALID pad, and can be seen in the above diagram.

Serial EEPROM

The Serial EEPROM used on the 912B32 board is a Microchip 25LC640, which is an 8k x 8 serial EEPROM that is SPI compatible. I have wired this part directly to the SPI port on the board, and it uses the SS pin of the SPI port as the chip select. If you wish, you can omit the serial EEPROM if you don't plan to use it.

If you do install the EEPROM, there are several cut jumpers that you can use to change the configuration. The default wiring works great when this device is the only thing on the SPI bus.

If your design plans to use the SPICON connector, then you may need to reconfigure the board so that the serial EEPROM uses a different chip select. The default wiring has the IC3's chip select connected to the SS pin on the SPI port. To change this, you will need to cut jumper JP1, and rewire a different chip select via an I/O output pin.

Two other pins are connected to defaults through cut jumpers. JP2 defaults the HOLD\ pin to high, and JP3 disables the write protect mechanism. You need to understand how the serial EEPROM works before changing these defaults.

Empty SMT layouts

The 912B32 board has a fairly large prototyping area for using standard through hole parts. I also included a few empty SMT layouts in some spare room I found on the backside of the board. These parts are labeled EMPTY1-4, and are available for your use.

In the above example, you will find that EMPTY1 has room for a standard SOIC-8 SMT part. I brought out each pin to a solder pad that will allow you to jumper it to other places on the board. I hope you find these useful.