Texas Instruments 990 User Manual page 90

Applications Programming
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2280121
Data returned by the SVC processor:
Sta tus/error cOde
System flags
DID, for read operations
SID, when set to zero by the applications program
BYTE 0
BYTE
2
BYTE 4
BYTE 6
BYTE 8
BYTE 10
BYTE 12
BYTE 14
BYTE 16
>40
STATUS CODE
I/O OPCODE
RESERVED
SYSTEM FLAGS USER FLAGS
I/O DATA BUFFER POINTERS
INPUT CHARACTER COUNT
OUTPUT CHARACTER COUNT
RESERVED
DID DID DID DID
SID
SID
SID SID
Figure 4-1 Supervisor Call Block for Input/Output Calls
The contents of the SVC block shown in Figure 4-1 are as follows:
Byte 0 contains the opcode >4D for the SVC.
Byte 1 contains the status/error code returned by the SVC.
The applications program should check the code and
take appropriate action. The codes and their
meanings are as follows:
Code Meaning
00 Operation requested bas been accepted by the
communications package.
01 I/O opcode function specified in byte 2 has
not been implemented.
4-4
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