ISDN TA POTS Interface

CMX625

 2001 Consumer Microcircuits Limited

8

D/625/2

1.5.2

Terminal Mode (TE)

Terminal mode (TE) frame structure consists of 3 channels of 4 bytes each repeated at 8kHz, i.e. 96 bits

in 125

µs or a data rate of 768kbps. The Data Clock (DCL) operates at twice the data rate, i.e. 1.536MHz.

Figure 3 shows the TE mode frame structure.

125µs

CHANNEL 0

CHANNEL 1

CHANNEL 2

B1

B2

MON0

C/I0

D

M

R

M

X

CHANNEL 0

IC1

IC2

MON1

C/I1

M

R

M

X

CHANNEL 1

TIC

CHANNEL 2

Not Used

Not Used

Not Used

DU/DD

FSC

DCL

M

S

B

L

S

B

FSC

= 8kHz

DCL

= 1.536MHz

DD, DU = 768kbps

Figure 3 Terminal Mode Frame Structure

‘Channel 0’ is used for passing user data (2B+D channels) and controlling (MON0 and C/I0) the Layer 1

transceiver. Only ‘Channel 1’ is used by the CMX625. ‘Channel 2’ is reserved for D channel arbitration.

The 12 byte frame contains the following channels:

(i)

The ‘B’ channels consist of two 64kbps data channels, labelled B1 and B2, and transfer B channel

data to and from the network.

(ii) The ‘Monitor’ channels consist of two programming channels, labelled MON0 and MON1. Each

channel consists of 8 bits of data and has two associated pair of handshake bits that control data

flow, MX and MR (monitor transmit and receive). The handshake procedure is described in section

1.5.4. The MON1 channel is used for programming and controlling devices attached to the IOM-2

interface. The CMX625 is programmed via the MON1 channel (see section 1.5.15). The MON0

channel is not used. Monitor channel contention is avoided by a “speak when spoken to” system

whereby the CMX625 is given a unique address, programmed with the 3 Slot Address pins (SA0 to

SA2) and 1 Device Select pin (DS) and only responds when that address is broadcast by the master

device (see section 1.5.14). The Monitor channel address byte is shown below:

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

MON Channel

Address

Byte

1

Slot

Address

SA2

Slot

Address

SA1

Slot

Address

SA0

Device

Select

DS

0

0

0