Technical information

Using NewBIOS Serial Solutions
RS232 handshake output lines, and to to set them via
subservice 1.
NewBIOS adds seven completely new services. These are.
Service ADH, Set port address.
Serial chips at the standard addresses defined by IBM for
COM1 and COM2 are automatically recognised by the
ROM BIOS (and hence NewBIOS) when the machine is
powered on or reset, but NewBIOS must be told of the
existence of chips at other addresses. This service returns
the address previously attributed to the port. It also returns
particular values as flags, so that this service can be used
to check for the presence of NewBIOS. The program
’NewBIOS.com’ uses this method to decide whether or not
to install NewBIOS.
Service AEH, Get number of ports.
The number of ports set up (ie with valid addresses) is
returned.
Service AFH, Get/Set IRQ line.
This service exists to support NewCOM, which can use
interrupts for more convenient and efficient serial
input/output. Subservice 0 returns the IRQ line which a
particular com port is assumed to be using, and subservice
1 sets this. Ports COM1 to COM8 are given default values
(which may need to be altered), but ports COM9 onwards
must be explicitly set before NewCOM can use them in
interrupt mode.
Service B0H, Get/Set Hardware Handshake.
This service exists to support NewCOM, which can use
several different hardware handshakes. The hardware
handshake is the way that the control lines associated with
a serial port are used. The input lines (CTS, DSR, DCD
and RI) are checked to ensure that it is ok to send data
out, and the output lines (RTS and DTR) are set to say
whether the driver has space to read any more data. The
handshake selected by this service defines which lines are
used, and how. This service also returns a flag to show
whether the driver is present, as opposed to simply
Chapter 4 Page 43