Document: LT0273

MX4428 MXP Engineering / Technical Manual

 

MXP Technical Description

In response to DISCON IN– going low, the microprocessor outputs a 10 msec pulse to DISCON OUT+, which applies “0V” to RL3 pin 16 through D5 and U8 pin 2, and “+24V” through Q11 to RL3 pin 1, thereby setting the relay contacts to their open state. When DISCON IN+ goes low the microprocessor outputs a 10 msec pulse to CONOUT, which applies “0V” to RL3 pin 1 through D6 and U8 pin 1, and “+24V” through Q10 to RL3 pin 16, thereby re-setting the relay contacts to the closed state.

The DISCON IN– signal is configured as an interrupt signal to the CPU. This allows a very fast response to it going low and ensures the relay is opened immediately. This is necessary as a short anywhere on the responder loop will often result in the responder power collapsing completely and the relay must be opened while sufficient charge remains in capacitors C64, C65, C66, and C59-C62.

When neither DISCON OUT+ nor CONOUT is high, no power is applied to the coil of RL3.

7.2.4.3MX4428 Communications Circuitry

The duplicated MX4428 communications channels are implemented using serial ports 1 and 2 of the 68302 CPU. The two transmit lines are isolated with optocouplers and buffered with Darlington drivers. The receive circuits are protected with series resistors and shunt diodes/capacitors, digitised with comparators, and isolated with optocouplers.

Passing messages around the loop is done entirely with software. For details of the MX4428 responder protocol and loop operation, refer to “F4000 Technical Manual - Appendix C, Responder Communication Protocol”.

7.2.5ANALOGUE LOOP INTERFACE

The Analog Loop (also known as MXP loop or NOSEx loop) is a two-wire circuit with the MXP being the master and up to 200 addressable devices which are slaves.

The MXP supplies the loop power (36 - 39V dc) which powers the addressable devices and sounder outputs. The loop + voltage is modulated with a 4V p-p dual frequency sinewave in order to transmit data using the power wire.

Both the MXP and the addressable devices transmit and receive in the same way. The addressable devices normally only transmit immediately after they have been polled by the MXP, however in special circumstances they can transmit interrupt messages when they have something urgent to send.

An example of a message on the loop is shown in Figure 7.2.

Issue 1.5

24 March 2006

Page 7-7

Page 91
Image 91
Tyco technical manual Analogue Loop Interface, 4.3 MX4428 Communications Circuitry

MX4428 specifications

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