=> R1 = &76 (reason code)
R2 = monitor lead ID
<= R1-R5 preserved to pass on
else
<= R1 = 0 (to claim service)
R2 preserved
R3 = default screen mode for this monitor type
R4 = monitor type
R5 = 0 => separate syncs
1 => composite sync
This service is issued by OS_ReadSysInfo 1 if the configured value for any of Mode, Monitor Type or Sync is "auto", to determine these parameters from the monitor lead. Older machines (e.g. A400 series vintage) cannot read monitor lead IDs
See PRM 1, page 625
Monitor lead IDs
The monitor conector has 4 ID pins (0 to 3). The connection of each pin is reported as a value:
Value ID pin is tied to
0 0v
1 +5v
2 Hsync
3 indeterminate
The connections of the 4 pins are reported in a bitfield:
Pin Bits
ID0 0,1
ID1 2,3
ID2 4,5
ID3 6,7
For example the portable module recognises that 1,1,1,1 occurs when no lead is connected, and sets mode 27, type 5, sync 0.
If the service is unclaimed RISC OS recognises the following values:
ID0 ID1 ID2 Type Sync Mode
H +5v +5v 0 (TV) composite 12
+5v +5v H 1 (Multisync) composite 27
+5v 0v +5v 3 (Mono VGA) separate 27
0v +5v +5v 3 (Colour VGA) separate 27
0v +5v 0v 4 (SVGA) separate 27
(Value of ID3 is not used)
If even this fails, RISC OS assumes type 0 - TV standard.
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