User`s guide

Use caution when you set SCB fields. Some of these parameters reflect the current
state of the operating system. If they are set to invalid values, software errors can
result. In general, do not use Function 49 to set a system parameter if another BDOS
function can achieve the same result. For example, Function 49 can be called to
update the Current DMA Address field within the SCB. This is not equivalent to
making a Function 26, Set DMA Address call, and updating the SCB Current DMA
field in this way would result in system errors. However, you can use Function 49 to
return the Current DMA address. The System Control Block is summarized in the
following table. Each of these fields is documented in detail in Appendix A.
Table 3-4. System Control Block
Offset -7 Description
00 - 04 Reserved For System Use
05 BDOS version number
06 - 09 User Flags
OA - OF Reserved For System Use
10 - 11 Program Error return code
12 - 19 Reserved For System Use
1A Console Width (columns)
1B Console Column Position
1C Console Page Length
1D - 21 Reserved For System Use
22 - 23 CONIN Redirection flag
24 - 25 CONOUT Redirection flag
26 - 27 AUXIN Redirection flag
28 - 29 AUXOUT Redirection flag
2A - 2B LSTOUT Redirection flag
2C Page Mode
2D Reserved For System Use
2E CTRL-H Active
2F Rubout Active
30 - 32 Reserved For System Use
33 - 34 Console Mode
35 - 36 Reserved For System Use
37 Output Delimiter
38 List Output Flag
39 - 3B Reserved For System Use
3-70
BDOS Function Calls CP/M 3 Programmers Guide