Asynchronous Adapter device driver

With the exception of the Get Version Number function call, when the device driver returns control to the calling program after a function call, a function call return code is returned in the AX register. These status codes are shown in Table 1.

Table 1. Function Call Return Codes in the AX Register
AX Register Contents	Description
00	Function call complete.
01	Function call unknown.
02	Asynchronous adapter not responding.
03	Library returns NACK to message.
04	Library not responding.
05	Communications not enabled.
06	Not used at this time.
07	Not used at this time.
08	No pending messages in receive message buffer.
09	Receive message buffer overrun attempted.
0A	Library failed to complete message it was sending.
0B	Library responded to command message with other than ACK or NACK.
0C	Asynchronous adapter failed to complete sending message to library.