System information

3400H + n = 980H, or n = 980H - 3400H
Assuming two's complement arithmetic, n = D580H, which can be checked by
3400H+D580H = 10980H = 0980H (ignoring high-order overflow).
Note that for larger systems, n satisfies
(3400H + b) + n = 980H, or
n = 980H - (3400H + b), or
n = D580H - b
The value of n for common CP/M systems is given below.
Table 6-2. Common Values for CP/M Systems
Memory Size BIAS b Negative Offset n
20K 0000H D580H - 0000H = D580H
24K 1000H D580H - 1000H = C580H
32K 3000H D580H - 3000H = A580H
40K 5000H D580H - 5000H = 8580H
48K 7000H D580H - 7000H = 6580H
56K 9000H D580H - 9000H = 4580H
62K A800H D580H - A800H = 2D80H
64K B000H D580H - B000H = 2580H
6.3 Second-level Regeneration CP/M Operating System Manual
6-8