Function Code 2 — Receive Character From The Serial Port - Zenith Z-100 Reference Manual

Page 8.10
Serial and Parallel Input/Output
Function Code 2 — Receive Character from the
Serial Port
Upon return from this call, bits 7, 4, 3, 2, and I of AH will contain the data
transfer status. Again, refer to Function Code 3. If AH is logic 0, the routine
reads a character properly into AL lf AH is not 0, some type of error occurred.
In a case such as this, time out errors refer to either the absence of the Data
Set Ready (DSR) or Clear To Send (CTS) signals.
Function Code 3 — Read Communications Status
This function permits interrogation of the communications interface status, the
condition of which is returned as a bit-mapped value in AX AH contains the
line control status and AL the modem control status, as shown by Tables 8.13
and 8.14.
Table 8.13. Line Control Status (Register AH)
BIT STATUS
Received data ready.
Overrun error.
The CPU did not read the previous character and a new character
has arrived.
Parity error.
Parity was enabled, but the parity of the incoming character did not
match.
Framing error.
An incorrect start/stop bit was received.
Break detect.
Transmitter holding register empty.
Serial I/O channel is ready for another character to transmit.
Transmitter shift register empty.
The serial VO channel is not currently transmitting.
Time-out error.
Device did not respond within a reasonable period of time.