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CMX867A

V.22 Full Duplex Call Set-Up on the CMX867

CML Microsystems Plc 

(f) Error handling has not been included since this aspect is implementation

dependent.

(g) The detection of in-band energy is indicated by b10 of the Status register

($E6). It is advisable to check this bit in both call set-up and data modes where

signals are due to be received since it is possible for noise to occasionally give

false indication of bit patterns on a line which does not in fact have a true

signal.

(h) The following bits in the Transmit Mode ($E1) and Receive Mode ($E2)

registers need to be set according to the circuit and function requirement:-

Tx Mode b11…b9 = Tx gain

Tx Mode b8,b7

= 550Hz/1800Hz Guard Tone enabling

Tx Mode b4…b0

= USART mode and format

Rx Mode b11…b9 = Rx gain

Rx Mode b5…b0

= USART mode and format

(i) Some points are shown on the drawing in Fig. 1 which relate to circuit

switching on the host external port (e.g. “Detect scrambled ONES in high

band for 270±40ms” is a point at which circuit 109 can be switched.)

(j) Register bit states on the flow charts assume a General Reset ($01) has been

issued and the normal start-up procedure has been followed prior to entering

the Calling and the Answering procedures. Each state during these two

procedures lists only the register bit changes that are required to move from

the previous state.

For both Calling and Answering modems:-

After connecting power to the modem:-

Write to the General Control ($E0) register

b7 = 1 (reset internal circuitry)

b8 = 1 (select normal operating mode)

Wait 20ms

2

Write to the General Control ($E0) register

b8 = 0 (powersave mode selected)

b6 = 1 (enable IRQN output)

b5 = 1 (unmask Ring Detect IRQ)

The modem is now in powersave mode but programmed to interrupt the

controlling micro controller when ringing is detected.

Proceed as shown in the flow charts for Calling Modem

For the Auto-Answering Modem when ring interrupt is serviced:-

Maintain the CMX867 in Powersave mode but monitor the Status register

($E6) to check the ring detect on/off timing. When valid ringing has been

received, proceed as shown in the flow charts for Answering Modem.

2. V.25 and V.14 implementation on the CMX867

2.1. V.25 timing has been included within figures 2 and 3. The only point not

covered is the optional transmission of 1300Hz by the calling modem in the

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