MT9171/72

Data Sheet

10

Zarlink Semiconductor Inc.

In MOD mode, DUAL port operation must be used and the D, B1 and B2 channel designations no longer exist. The

selection of SLV or MAS will determine which of the DNICs is using the externally supplied clock and which is

phase locking to the data on the line. Due to jitter and end to end delay, one end must be the master to generate all

the timing for the link and the other must extract the timing from the receive data and synchronize itself to this timing

in order to recover the synchronous data. DUAL port mode allows the user to use two separate serial busses: the

DV port for PCM/data (B channels) and the CD port for control and signalling information (C and D channels). In the

SINGL port mode, all four channels are concatenated into one serial stream and input to the DNIC via the DV port.

The order of the C and D channels may be changed only in DN/DUAL mode. The DNIC may be configured to

transfer the D-channel in channel 0 and the C-channel in channel 16 or vice versa. One other feature exists; ODE,

where both the DV and CD ports are tristated in order that no devices are damaged due to excessive loading while

all DNICs are in a random state on power up in a daisy chain arrangement.

DV Port (DSTi/Di, DSTo/Do)

The DV port transfers data or PCM encoded voice to and from the line according to the particular mode selected by

the mode select pins. The modes affecting the configuration of the DV port are MOD or DN and DUAL or SINGL. In

DN mode the DV port operates as an ST-BUS at 2.048 Mbit/s with 32, 8 bit channels per frame as shown in Figure

9. In this mode the DV port channel configuration depends upon whether DUAL or SINGL port is selected. When

DUAL port mode is used, the C and D channels are passed through the CD port and the B1 and B2 channels are

passed through the DV port. At 80 kbit/s only one channel of the available 32 at the DV port is utilized, this being

channel 0 which carries the B1-channel. This is shown in Figure 3. At 160 kbit/s, two channels are used, these

being 0 and 16 carrying the B1 and B2 channels, respectively. This is shown in Figure 4. When SINGL port mode is

used, channels B1, B2, C and D are all passed via the DV port and the CD port is disabled. See CD port description

for an explanation of the C and D channels.

Figure 9 - ST-BUS Format

The D-channel is always passed during channel time 0 followed by the C and B1 channels in channel times 1 and

2, respectively for 80 kbit/s. See Figure 5. For 160 kbit/s the B2 channel is added and occupies channel time 3 of

the DV port. See Figure 6. For all of the various configurations the bit orders are shown by the respective diagram.

In MOD mode the DV and CD ports no longer operate at 2.048 Mbits/s but are continuous serial bit streams

operating at the bit rate selected of 80 or 160 kbit/s.

While in the MOD mode only DUAL port operation can be used.

In order for more than one DNIC to be connected to any one DV and CD port, making more efficient use of the

busses, the DSTo and CDSTo outputs are put into high impedance during the inactive channel times of the DNIC.

This allows additional DNICs to be cascaded onto the same DV and CD ports. When used in this way a signal

called F0o is used as an indication to the next DNIC in a daisy chain that its channel time is now active. Only the

first DNIC in the chain receives the system frame pulse and all others receive the F0o from its predecessor

in the chain. This allows up to 16 DNICs to be cascaded.

Channel

0

Channel

1

Channel

2

• • • • • • • •

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

125

µsec

Channel

31

Channel

30

Channel

31

Channel

0

Channel

29

F0

ST-BUS

Most

Significant

Bit (First)

Least

Significant

Bit (Last)

3.9

µsec