Maxim Integrated MAXQ Family - Manual (Page 30)

3-5
8-bit destination ← high byte (16-bit source)
If, however, we needed to load an 8-bit register with the high byte of a 16-bit source, it would be best to use the GR register. Transferring
the 16-bit source to the GR register adds a single cycle.
move GR, LC[0] ; move LC[0] to the GR register
move IC, GRH ; copy the high byte into the IC register
16-bit destination ← concatenation (8-bit source, 8-bit source)
Two 8-bit source registers can be concatenated and stored into a 16-bit destination by using the prefix register to hold the high-order
byte for the concatenated transfer. An additional cycle may be required if either source byte register index is greater than 0Fh or the
16-bit destination is greater than 07h.
move PFX[0], IC ; load high order source byte IC into PFX
move @++SP, AP ; store @DP[0] the concatenation of IC:AP
; 16-bit destination sub-index: dst=08h
; 8-bit source sub-indexes:
; high=10h, low=11h
move PFX[1], #00h ;
move PFX[3], high ; PFX=00:high
move dst, low ; dst=high:low
Low (16-bit destination) ← 8-bit source
To modify only the low byte of a given 16-bit destination, the 16-bit register should be moved into the GR register such that the high
byte can be singulated and the low byte written exclusively. An additional cycle is required if the destination index is greater than 0Fh.
move GR, DP[0] ; move DP[0] to the GR register
move PFX[0], GRH ; get the high byte of DP[0] via GRH
move DP[0], #20h ; store the new DP[0] value
; 16-bit destination sub-index: dst=10h
; 8-bit source sub-index: src=11h
move PFX[1], #00h ;
move GR, dst ; read dst word to the GR register
move PFX[5], GRH ; get the high byte of dst via GRH
move dst, src ; store the new dst value
High (16-bit destination) ← 8-bit source
To modify only the high byte of a given 16-bit destination, the 16-bit register should be moved into the GR register such that the low
byte can be singulated and the high byte can be written exclusively. Additional cycles are required if the destination index is greater
than 0Fh or if the source index is greater than 0Fh.
move GR, DP[0] ; move DP[0] to the GR register
move PFX[0], #20h ; get the high byte of DP[0] via GRH
move DP[0], GRL ; store the new DP[0] value
; 16-bit destination sub-index: dst=10h
; 8-bit source sub-index: src=11h
move PFX[1], #00h ;
move GR, dst ; read dst word to the GR register
move PFX[1], #00h
move PFX[4], src ; get the new src byte
move dst, GRL ; store the new dst value
If the high byte needs to be cleared to 00h, the operation can be shortened by transferring only the GRL byte to the 16-bit destination
(example follows):
move GR, DP[0] ; move DP[0] to the GR register
move DP[0], GRL ; store the new DP[0] value, 00h used for high byte
MAXQ Family User’s Guide
Maxim Integrated