Page 180 - Programming Microcontrollers in C

Microcontroller Memory 165

code, 0xd7, to do a store the accumulator indexed with a 16-bit offset
is created at the location 0x56 in memory. The 16-bit offset is the
address passed to the function in the combination of the x register and
the accumulator. This address is placed in the memory locations 0x58
and 0x57, completing the store instruction. At the address 0x59, a re­
turn from subroutine instruction, 0x81, is placed to complete the
function. The index register is cleared, and this two-instruction sub­
routine is executed to store the appropriate data prior to the program
setting the latch bit.

void erase(int* x)
0052 {
0815 BF 52 STX $52
0817 B7 53 STA $53
0819 12 07 BSET 1,$07 EEPROM_CTL.E1LAT=1;
081B 14 07 BSET 2,$07 EEPROM_CTL.E1ERA=1;
081D B7 58 STA $58 *x=0;
081F 9F TXA
0820 B7 57 STA $57
0822 4F CLRA
0823 AE D7 LDX #$D7
0825 BF 56 STX $56
0827 AE 81 LDX #$81
0829 BF 59 STX $59
082B 5F CLRX
082C BD 56 JSR $56
082E 10 07 BSET 0,$07 EEPROM_CTL.E1PGM=1;
0830 5F CLRX delay(PROG_TIME);
0831 A6 0A LDA #$0A
0833 CD 00 00 JSR $****
0836 13 07 BCLR 1,$07 EEPROM_CTL.E1LAT=0;
0838 81 RTS }
This code sequence requires 36 bytes, plus 4 bytes of uncommit­
ted RAM space, to accomplish what required 22 bytes in the earlier
example of the same operation.
You must not avoid the use of pointers because of this one ex­
ample. There are cases when proper pointer usage will provide the
best code that you can generate. When writing code for
microcontrollers, use many relatively small functions that you can