Interface Circuitry; Bi-Directional Lines; Output Signals; 5-Volt Regulator - Tait TM9100 Service Manual

Table 3.3 Connector power supply options
Link state
LK7
LK5 LK6
(R787)
out out out
in out in
out in in
in out out
out in out
in in/out in
3.7

Interface Circuitry

For a block diagram of the interfaces circuitry, refer to
Introduction
For more on the connector pinouts, refer to
Bi-directional lines are provided on four pins of the auxiliary connector,

Bi-directional Lines

(
AUX GPIO
seven on the internal options connector (
the auxiliary and control-head connectors are formed by combining two
uni-directional lines. For example, the line
auxiliary connector is formed from
The circuitry is the same in all five cases and is explained below for the case
of
An output on the line

Output Signals

(e.g. 4)
AUX GPIO
from the digital section. The signal is first inverted by Q703 (pins 3 to 5) and
the output divided down to 1.6V by R746 and R753 to drive the base of
Q703 (pins 1, 2 and 6). When the latter's collector current is low, the base
current is a maximum and creates a small voltage drop across R761, causing
the collector emitter to saturate. As the collector current increases, the base
current decreases proportionally until the voltage across R761 reaches 1V.
At this point the base-emitter begins to turn off and the base current
diminishes rapidly. The net effect is a current-limiting action. The current
limit value is approximately 18mA (the inverse of the value of R761).
The output configuration is open-collector with a pull-up to 3.3V by
default. Pull-up options to 5V and 13.8V are also available. On
only, the optional MOSFET Q707, which has a high current drive, may be
fitted.
The 5V supply mentioned above is provided by a simple buffered zener

5-Volt Regulator

regulator formed by Q702, D721, R721 and R722. The resistor R722
limits the current to about 25mA under short-circuit conditions.
86 Circuit Descriptions
Connector power state
LK8
Auxiliary
(R786)
out switched
out switched
out switched
in switched
in switched
in unswitched
4 to 7) one on the control-head connector (
AUX GPIO
4.
AUX GPIO
AUX GPIO
Internal
Control head
options
no power no power
switched switched
switched unswitched
unswitched switched
unswitched unswitched
unswitched unswitched
"Connectors" on page
1 to
IOP GPIO
4 at pin 10 of the
AUX GPIO
4 and
ITF AUX GPI DIG AUX GPO
4 originates as the 3.3V signal
© Tait Electronics Limited August 2005
Microphone
no power
switched
unswitched
switched
unswitched
unswitched
Figure 3.9.
34.
1), and
CH GPIO
7). Those on
IOP GPIO
4.
4
DIG AUX GPO
4
AUX GPIO
TM9100 Service Manual