Herald 4 port 4 wire Terminal Card

1A1/SA20006- YELLOW Handle

This card can run 4 4 wire terminals or 4 2 wire POTS phones

The D4071 crosspoint ICs

This card can switch audio from any one of the Herald's 20 2 wire speech highways to any of the attached 4 telephones. It does this with 4 integrated circuits, each able to connect 2 of the phones to 10 of the speech highways. Each D4071 is passed commands from the processor card, via the backplane and finally from the control IC via the XPT lead.

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The Ring Relay

Conventional POTS type ringing is used to alert a two wire POTS phone extension user to an incoming call.

The ring current is not carried on any of the Herald's 20 highways, instead the 25 Hz ring current, generated by the tone card is carried to all the left hand slots, each card has a 4 ring relays to direct the ring current to the appropriate extension telephone.

The D4073 Control IC

The relays and crosspoint on the terminal card itself and the LEDs, tone caller on the 4 terminals attached to the card are controlled from the Herald's processor card located on the right hand side of the top shelf close to the power supply.

Terminals equipped with loudspeaking amps and headsets can also be controlled via the above method fro the LEDs

Part of the processors address bus:- R/W,A0,A1,A13

and a CE (Card enable) signal and serial DFM (data from micro) signal are processed by the four Control ICs pictured below.

The state of the terminals hookswitch and press buttons as well as the loop and earth recall detectors on the card are also communicated via these control ICs and via the the serial DTM (data to micro) signal back to the processor.

There are 2 pairs which form the interface between the terminal card and each terminal

1 pair carries (the speech pair) the speech and ring current, the other pair carries the push button and hookswitch states from the terminal and LED states to the terminal.

In the event of a mains power failure an exchange line is switched directly to a terminal via the speech pair, so that the signals on the speech pair are very similar to a POTS line.

Power

The terminal interface card is supplied with the following DC power via the backplane connector

-50VSpeech,-50VData,-12V,+12v,+5v,+1.5, ov

When the herald is powered the terminal card supplies DC to the terminal over the data pair that all times except when a short on that pair is detected.

The things I don't know

When the herald is powered the terminal card supplies DC to the terminal over the speech pair that all times (inc when ringing) ?

When the herald is powered the terminal card supplies DC to the terminal over the data pair at all times ?

When the herald is powered both internal and external ringing is signalled to the terminal by ring current or over the data pair ???

When the herald is powered dialled digits are signalled back to the terminal card over the data pair or by 10 pps on the speech pair ???

The Data Transformers

Both the data pair and speech pair need transformers, below are the four data transformers on the card

Back Plane Connector

Thanks to Mike for sending me some pictures on later versions of this card

SA20557 4 port 4 wire Terminal Card (featurephone)

This card allows up to to four system phones or POTS telephones in the Pentara System is provided by this 4-circuit, 4·wire Extension Card.

Connections to system phones are made via a speech pair line and a

data pair line, POTS telephones are connected to the speech

pair lines only. Display data is provided for the use of

system phones having the Display feature.

BLOCK DIAGRAM of 4 x 4 WIRE EXTENSION CARD

Digital Communications with system phone

DATA CIRCUITS

There are four Data Circuits on each 4-wire Extension Card., one to each Terminal. The circuits are identical

Data Transmission

Data sign all ing between the Extension Card and the Terminals is by biphase serial data transmission at 1.2kHz. LED data or display data is transmitted to the Terminal and keycode data is received from the Terminal.

The data pai r (Data Line 1) to a Terminal is coupled to the Terminal Interface Data IC (lC15) via trans­mitter circuit IC2(a). TR5 and T3. The transmitter circuit combines the outputs from IC15 (TXOA and TXOB) into a biphase signal by differential amplifier IC2(a). This differential mode allows the first transition to be half that of subsequent ones, thus preventing an initial voltage offset which would cause the receiver at the Terminal to miss the first few transitions.

DATA TRANSMISSION TO A TERMINAL

Data transmission to a Terminal is initiated by a "Control Load" command from the Processor. The

Data IC reads the LED data from the appropriate locations in the RAM and sends it to the Data Circuit from the TX outputs. If the Terminal requires display data this is transmitted after the LED data, refer to para 4.6.2. If the Retransmit Request Latch (RRL) in the Data IC is set, the control word sent before the LED data is set to 111 1, the R R L is then reset.

Figure 4.2 shows a typical biphase waveform.

The output of IC2(a) drives TR5 to apply the signal to the data line via T3, maximum peak-to-peak volt­age is 0.85V and the transmission rate is 1.2kHz.

LED/DISPLAY DATA transmitted to terminal

A LED data transmission consists of a preamble byte (6 Hex), a control byte'and four LED data words of 2 bytes each, the transmission is completed by a post-amble bit (0). The control byte consists of two hexa-decimal characters, the first character is either 0 for a normal transmission or F (Hex) for a re-transmit request, the second character is 4 to indicate that 4 LED data words follow (see Figure 4.8).

A display data transmission is similar to a LED data transmission, but has the second character in the control byte = C (Hex) to indicate that there are 8 display words (2 bytes each) in addition to the 4 LED data words. The transmission is completed by a post-amble bit (0) (see Figure 4.9).

Data Re c e p t i o n

The incoming biphase data signals on Data Line 1 from a Terminal are connected via T3 and C6 to the Schmitt trigger circuit IC9(al. R24, R32 and R40.

The Schmitt trigger circuit has a hysteresis of approximately 0.2V. R 10, R13 and C3 provide the reference voltage for all four data circuits. The detected data signals are output on the RXO line from IC9(a) to the Data IC (IC15).

RECEIVING DATA FROM A TERMINAL

After the LED data (and display data) has been sent to a Terminal the Data IC waits for keycode data from that Terminal on the RX input. Should the preamble and control byte not be received within 2 frames the terminal type counter (TTC) will have reached a count of 2 and the code T000 0000 will be sent to the Speech IC (where T = 0). When the preamble and control byte are received the TTC is reset,

the Data IC then waits for the keycode and the key-code complement_ Should the keycode not be received or should the keycode not match the complement, the R R L is set and the code TOOO 0000 will be sent to the Speech IC (where T = 1) _ When the keycode data is correctly received the code TKKK KKKK will be sent to the Processor (where T= 1 and KKK KKKK is the keycode).

Data Power Supply

The data pair is f e d via Darlington transistor T R 7 and T3 secondary windings. Signal DP1 active from the Speech IC (IC14) turns on TR3 to drive TR7 on and connect the -50VD supply to the data line via T3 winding 4/5. OV is connected to the c leg via T3 w inding 1/2. Diode D13 protects TR7 against the back emf across T3 when TR7 turns off. R62 and R64

protect the data pair against over voltage.

Data Power Supply Short Circuit Detection

The current through the secondary windings of T3 is monitored by resistor network RU1(a) and level comparator IC1(a). Should the current exceed 90-250mA, IC1 (a) output switches low to generate signal SC1 active to the Speech IC (IC14). IC1 (a) output goes high when the current is not greater than 90mA.

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