from the datasheet "In the DS89C430, the MOVX instruction takes as little as two machine cycles or two oscillator cycles"

MOVX A,@dptr
MOVX @dptr,A

instruction pairs, the whole thing takes 60 ns per byte

nope, 2*2/33M = 121ns
excluded as Richard did: djnz

now comparing to a f120 with pagebound buffers
movx A,@R0 3 cycles
MOVX @dptr,A 3 cycles
inc R0 1 cycle
for a total of 70ns

excluded as Richard did: djnz

if you write the buffer backwards and use the same register for @R1 and djnz you can cut it to 60ns


Erik