Msg: 5626 *Conference*
01-05-95 16:33:56
From: RON WIESEN
To : COMET _
Subj: REPLY TO MSG #5618 (F647 (63047))
F647h/63047/-02489 is a temporary holding cell used when an Escape X sequence (027,088) for the Liquid Crystal Display (LCD) is processed. In the process, the content of F647h/63047/-02489 is copied to F646h/63046/-02490 and then F647h/63047/-02489 is cleared. The code that does this is shown below. 444Ah/17482/-48054 LXI H, F647h MOV A, M MVI M, 0 ;clear holding cell DCX H ;HL=F646h/63046/-02490 MOV M, A RET Linkage to 444Ah/17482/-48054 is in the last 3-byte entry of the LCD escape sequence lookup table. This entry is shown below. 43F7h/17399/-48137 DB 'X' DW 444Ah ;link address for Escape X sequence I would guess that escape sequence processing for the LCD, and normal LCD processes, are tied to the 4.0 millisecond clock interrupt (RST 7.5) handler. So unless your REAL FAST, the content of the holding cell will become cleared before you get a chance to PEEK it. This is a guess, but you could verify this with some m/l code that disables interrupts and then alters and inspects the holding cell.