I
MDR-2000 VJ User's Reference Manual
Communications
4.5 Data Transmission
The MDR-2000 utilizes asynchronous data transmission techniques. It
is
programmed for 8 data
bits, no parity, and 1 stop bit. Except for the specific cases described below, only 7
of
the 8 data
bits are actually used, the high order bit being removed under software control. Note however that
the MDR-2000 is programmed to receive 8 data bits and therefore any communications equipment
interfacing with the MDR-2000 must be programmed accordingly.
In the situation where parity
is
forced on the data, and therefore only 7 data bits are possible (as in
some public packet switching services), communications with the MDR-2000 is still possible. This
is accomplished by noting that the MDR-2000 never sends a packet larger than 127 data bytes in
any
of
its current configurations. This means that the byte count never occupies more than 7 bits.
In addition the two 8-bit checksum bytes (16-bit checksum) can be treated as two 7-bit checksum
bytes.
4.6 LED Indicators
To provide immediate djagnostic and operational feedback a series
of
8 LED indicators are used by
the MDR-2000. These indicators are designated CR2 thorough CR9 on the circuit boards. Their
meanings are listed on the table below. On units where they are externally visible the external
labels are denoted in the table.
When all
of
the LEDs are on simultaneously the MDR-2000
is
in the initialization sequence. The
troubleshooting section
of
this manual contains more information on the interpretation
of
these
LED's.
When CR7
is
flashing, but not constantly on, the MDR-2000 has reached its call threshold setting
(see SET THRESHOLD command in Chapter 5). When CR7 is constantly on then the buffer is full
and calls are being discarded.
4-9
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