Maxim Integrated MAXQ7666 User Manual
Page 377
MAXQ7665/MAXQ7666 User’s Guide
15-8
15.5 ROM Example 2: Calling A MAXQ7665 Utility ROM Function Indirectly
The second example shows the indirect addressing method (lookup table) for calling MAXQ7665 utility functions. We use the same
function (UROM_MoveDP1Inc) to read our static string, but this time we must figure out the address we want dynamically. Note the
inserted code where we before had a direct call to the function. Also note that the function index of moveDP1inc is 7.
Text:
DB “Hello World!”,0
; Define a string in code space.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Function:
PrintText
;; Description:
Prints the string stored at the “Text” label.
;; Returns:
N/A
;; Destroys:
ACC, DP[1], DP[0], and GR.
;; Notes:
This function assumes that DP[0] is set to word mode, and
;;
DP[1] is in byte mode.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
PrintText:
move DP[1], #Text
; Point to the string to display.
move ACC, DP[1]
; “Text” is a word address and we need a
sla
; byte address, so shift left 1 bit.
or #08000h
; Code space is mapped to 8000h when running
move DP[1], ACC
; from the ROM, so the address must be masked.
PrintText_Loop:
;
; Fetch the byte from code space.
;
move DP[0], #0800Dh
; This is where the address of the table is stored.
move ACC, @DP[0]
; Get the location of the function table.
add #7
; Add the index to the moveDP1inc function.
move DP[0], ACC
; Point to where the address of moveDP1 is stored.
move ACC, @DP[0]
; Retrieve the address of the function.
call ACC
; Execute the function.
move ACC, GR
jump Z, PrintText_Done
; Reached the null terminator.
call PrintChar
; Call a routine to output the char in ACC
jump PrintText_Loop
; Process the next byte.
PrintText_Done:
ret
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