This program displays the contents of the bootstrap ... - Matthieu Benoit
This program displays the contents of the bootstrap ROM in a Motorola ... fetch a byte from the bootstrap area, invert it and display on 8 LEDs loop: lda ... Page 3 ...
;This program displays the contents of the bootstrap ROM in a Motorola MC68705P3 or P5 microcontroller. It can be modified to do the same with ;the MC68705U3, U5, R3 and R5. I haven’t tried but it should be possible to modify it for other Motorola microcontrollers ;To setup the hardware you can place the microcontroller on a breadboard and connect XTAL pin to the EXTAL pin (to use RC mode) ;Connect nine LEDs as follows – connect all the LED anodes to +5V ;Connect each LED cathode to its own 1K resistor and connect the other side of 8 resistors to Port A; connect the 9th resistor to bit 7 of Port B ;The 8 Port A LEDS will display each byte of data, the 9th LED acts as a ‘data ready’ signal ;The idea is each time the ‘data ready’ LED flashes you need to quickly write down the value being displayed on the 8 data LEDs ;If you miss any values don’t worry, just keep going, you can re‐run the program and fill in the missing values later. The circuit can be improved by ;using BCD to 7‐segment decoders and 7‐segment displays but since it normally is only used once it’s hardly worth the trouble ;An alternative is to remove all the delay loops in the program and feed the Port A and ‘data ready signals into an I/O card connected to a computer ;or other microcontroller and have it log the data ;originally written by Peter Ihnat in May 2012 ;properly documented in Feb 2016; also added references to MC68705S3 but I haven’t tested it on an S3 micro ;equates PortA equ 0000H PortB equ 0001H ;data direction registers DDRA equ 0004H DDRB equ 0005H ;variables used by delay subroutine org 0010H ;note: for MC68705S3 use 0018H instead of 0010H cntr rmb 1 cntr1 rmb 1 ;********************* ;main program starts here ;(at start of EPROM) ;*********************
org 0080H Start: rsp ;setup I/O ports ‐ Port A displays a byte of data on 8 LEDs ;a ‘data ready’ LED connected to bit 7 of Port B is flashed when correct data is displayed on Port A ;note: outputting a 0 turns on an LED, 1 turns it off ;first setup Ports A and B as outputs and set all bits high (LEDs off) lda #0FFH sta PortA sta DDRA sta PortB sta DDRB clrx ;reg X will be used as an offset to access each value in the bootstrap area clr cntr ;used in delay subroutine ;fetch a byte from the bootstrap area, invert it and display on 8 LEDs loop: lda 0785H,X ;note that address 0785H is the start of the bootstrap ROM for the MC68705P3 and P5 ;for the MC68705U3, R3, U5 and R5 use 0F80H ;for the MC68705S3 use 0F20H coma sta PortA ;flash ‘data ready’ LED bclr 7,PortB ;turn LED on bsr delay bset 7,PortB ;turn LED off bsr delay ;increment pointer to the next byte incx cpx #73H ;check if end of bootstrap code has been reached ;note that 73H (115 bytes) is the length of the bootstrap ROM for the MC68705P3 and P5 ;for the MC68705U3, R3, U5 and R5 use 120 bytes or 78H
;for the MC68705S3 use 216 bytes or 0D8H bne loop bra * ;all done so go into infinite loop ;************ ;SUBROUTINES ;************ ;this is a very simple delay routine. Increase the value #30H if you want the data to be displayed on the LEDs for a longer time delay: lda #30H sta cntr1 del: bsr wait dec cntr1 bne del rts wait: bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr bsr deccntr deccntr: dec cntr bne deccntr rts
;********** ;vectors, etc ;********** ;interrupts (not used here) Timer: rti Ext: rti SW: rti ;set MOR so micro is in RC mode org 0784H ;use address 0784H for the MC68705P3 and P5 ;use address 0F38H for MC68705U3, U5, R3 and R5 ;use address 0F1EH for MC68705S3 fdb 80H ;setup all the vectors for correct operation org 07F8H note that address 07F8H is the location of vectors for the MC68705P3 and P5 ;for the MC68705U3, R3, U5 and R5 use 0FF8H ;for the MC68705S3 use 0FF8H fdb Timer ;vector to Timer interrupt routine fdb Ext ;vector to External interrupt routine fdb SW ;vector to SW interrupt routine fdb Start ;vector to start of main program
from that memory location. In the P3 the 2 bytes are 07H and 85H which, as expected, is the starting address of the Bootstrap ROM (0785H). However in the P5 ...
The first listing is the Bootstrap ROM exactly as it appears in the 68705U3 ... Just before the program reads the external EPROM it checks the INT input (pin 3). If.
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