Technical information

Serial Solutions NewBIOS Reference
Service 3H, read status.
The state of the RS232 handshake input lines and the
status of the serial chip (including things like reception
errors, chip ready to send data) are returned. The other
standard services return some or all of this information
anyway.
Service 4H, extended initialise.
Provided on the PS/2 ROM BIOS (and on NewBIOS for
all PCs), this performs a similar function to service 0H, but
allows a wider range of parameters to reflect the full
capabilities of the serial chip and is somewhat easier to
use. The NewBIOS version extends the ranges of baud
rates available still further.
Service 5H, extended communications port control.
This allows us to read, via subservice 0, the state of the
RS232 handshake output lines, and to to set them via
subservice 1.
NewBIOS adds the following completely new services.
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.
Page 72 Chapter 5