Er.
The first 22 instructions in the reset vector unambiguously include a loop that clears all internal RAM:
Code:
_Reset $85AF 78: sei
$85B0 D8: cld
$85B1 A9 00: lda #$00
$85B3 8D 00 20: sta $2000
$85B6 A2 FF: ldx #$FF
$85B8 9A: txs
- $85B9 AD 02 20: lda $2002
$85BC 29 80: and #$80
$85BE F0 F9: beq - ; $85B9
- $85C0 AD 02 20: lda $2002
$85C3 29 80: and #$80
$85C5 F0 F9: beq - ; $85C0
$85C7 A0 07: ldy #$07 ; loop that clears memory starts here, with address 0x700
$85C9 84 01: sty $01
$85CB A0 00: ldy #$00
$85CD 84 00: sty $00
$85CF 98: tya
- $85D0 91 00: sta ($00),y
$85D2 88: dey ; counting down, so 700 7FF 7FE &c
$85D3 D0 FB: bne - ; $85D0
$85D5 C6 01: dec $01 ; counting down, so 700 600 500 &c
$85D7 10 F7: bpl - ; $85D0