Beijer Electronics Fax 801-466-8792 Web www.beijerelectronicsinc.com Phone 801-466-8770
C
HAPTER
4.
QTERM S
ERIAL
M
ODES
4.1
Serial Modes
Regardless of the serial interface hardware selected, the
QTERM software can operate in three different serial inter-
face modes: Full-Duplex, Block and Multidrop Modes.
These serial modes can be selected from within either
Power-On Setup mode or the QDATA file by setting the
[serial mode] field.
Not all serial modes are useful with all of the different types
of serial interface hardware available with the QTERM. For
example, Full-Duplex mode is not useful with an EIA-485
hardware interface.
Block Mode is very similar to Multidrop Mode. If your
QTERM is a Multidrop unit, we recommend that you read
the Block Mode section before reading the Multidrop sec-
tion.
4.2
Full-Duplex Serial Mode
When in Full-Duplex serial mode, the QTERM immedi-
ately executes key strokes as they are pushed. Host mode
string data is sent to the host and local mode data, and com-
mands and special functions are executed when the key is
pressed. Commands are executed and displayable data is
displayed as soon as they are received from the host. Only
one terminal may be connected to the host.
Full-Duplex may be used only with the following hardware
interfaces: EIA-232, -422, and 5-volt Buffered.
Xon/Xoff handshaking is supported and is only available in
Full-Duplex mode. If desired, Xon/Xoff handshaking can
be disabled from within the QDATA file.
4.3
Block Serial Mode
Block Serial Mode is useful for prompt/response systems
with semi-intelligent hosts where the user must construct a
complete, correct response at the QTERM, prior to trans-
mission, without host intervention.
In Block Mode, all communication between the Host and
the QTERM is done with data packets. A valid Block Mode
data packet consists of a data portion followed by a user-
definable, End-Of-Packet (EOP) terminator character. The
data portion may contain any number of displayable or
command data bytes, but must not contain a byte equal to
the EOP character. The EOP character is user-definable in
the QDATA file; any 8-bit value is valid.
Block Mode may be used only with the following hardware
interfaces: EIA-232, -422, and 5-volt Buffered.
Since Block Mode is not a full-duplex scheme, the QTERM
cannot simultaneously process incoming data from the host
and keystrokes. This does not mean that data will be lost,
but it does mean that the host software must support the
communications scheme described below.
In order to understand the operation of Block Mode (and
Multidrop Mode), you must understand the following ter-
minology:
DATA PACKET
A formatted sequence of bytes which must be used to trans-
mit data to and from the QTERM running in Block Mode.
The format is very simple. All Data Packets consist of a
free-form data portion followed by an EOP Terminator
(described below). The data portion consists of a stream of
bytes and may be as long as desired, but it may not contain
a character equal to the EOP Terminator. The data portion
must always be followed by the EOP Terminator.
EOP TERMINATOR
A special character, defined in the QDATA file, which per-
forms two functions. It terminates all Data Packets sent
from and received by the QTERM when in Block Mode. It
is also used to terminate EDIT Mode and causes the EDIT
Buffer to be sent to the host when a key, defined with the
EOP Terminator character, is pushed. If you wish to use
Block Mode, you must define at least one key with the EOP
Terminator.
