Go to EE395 Experiment   1     2     3    4    5        Microprocessor board      8251A Interface     SBC      ECE Lab home

The EEPROM Monitor Program

To get this microcomputer to operate it is necessary to put a monitor program into an EPROM or EEPROM. This design uses a 28C256 EEPROM because it is suciently large to accommodate the program that we wish to use as a system MONITOR. This is the monitor program that has been quite thoroughly reworked by Dave Harrison and myself. The program MON208.ASM can be found on the computers that are connected to the programming stations in the 204F, 211F and 318F laboratories in the hard drive subdirectory \ASM68K. Antonakos’s latest assembler and emulator are there as well. The monitor program is assembled using Antonakos’s assembler. The resultant .HEX file is then used to burn the EEPROM as described in the next section.

Follow the construction tips found on page 367 of Antonakos’s book. If difficulties are encountered in getting the board to come alive, you may try a few troubleshooting techniques.

• All digital ICs must have a bypass capacitor connected from Vcc to ground. This gives them a local reservoir of charge for their current draw demands, which take place in fits and starts.

Mount all devices in wire wrap sockets. That includes the DIP switch, the LED display and the 4MHz oscillator can. Wiring should be neat and close to the board. Use insertable wire wrap pins if it looks like you don’t have enough room on some pin for all the wire wraps that you need. If you project looks like a rat’s nest when it is finished then you will surely have problems troubleshooting it.

• Make sure each chip is connected to V_cc and ground.

• Buzz out all of your connections with a continuity tester. Do this before you insert the chips.

• Make sure all chips have been installed in their sockets correctly.

• There is no need to interface your SBC to a PC for this test.

Write a short MONITOR program, taking care of the first two vectors that have to be put in memory followed by a routine that reads the DIP switches and outputs the settings on the LEDs. The MONITOR should follow the pattern below

pport      equ      $18000
stack      equ      $10000
           org      0
           dc.l     stack
           dc.l     here
here       move.b  |pport,pport
           bra.s    here
           end

If this parallel port test works then it means that the SBC is working with the exception of the serial port. To test it see below.

• If the above doesn’t work or the MONITOR refuses to sign on, simply burn the following code into the EEPROM.

stack       equ      $10000
            org 0
            dc.l     stack
            dc.l     here
here        bra.s    here
            end

There is no need to interface your SBC to a PC for this test. If the CPU is running then you should be able to see a periodic signal on the lower address lines and the data lines. You should determine ahead of time what it is you expect to see on the various data, address and control lines and check if that is what you have on the oscilloscope or the logic analyzer.

• If the parallel port test is successful then test the serial port by burning the SERTEST program into the EEPROM and see if you get anything interesting on the PC screen.

• If the above prove fruitful then you are ready to install the full monitor program and finish the project.

Programming the EEPROM Monitor

There are PCs in room 204F, 211F as well as in room 318F, which are interfaced with Xeltek programmer pods. To burn the EEPROM go to the \SP\BIN   subdirectory and type SP<ent> then follow the steps below.

• Type <F9> to select the programming of GALs or EEPROMs, and then <esc> to get out.

• Type <F7> and use < * > <ent> to select the device manufacturer, and then <esc> to get out.

• Type <F8> and use < * > <ent> to select the device number, and then <esc> to get out.

The proper data for the EEPROM should now appear in the right middle of the screen. Use the FILE menu to load the .HEX file that you will need to program the chip. Use the BUFFER, EDIT feature to verify the data that has been loaded, assuming that you have taken the trouble to memorize a few bytes of your code.

Go to the DEVICE screen to program the chip. It is self explanatory from here.

If your EEPROM fails to program under its proper brand name, then program it as a XELTEK 28C256 chip. No harm is done since all the programming is done by toggling 5 volts on and off at various pins.

Go to EE395  Experiment    1     2     3    4    5       Microprocessor board      8251A Interface     SBC     ECE Lab home