73M1866B/73M1966B Data Sheet
DS_1x66B_001
FS
PCLK
DX
MSB
LSB
Figure 21: 16-bit Transmission Example
Similarly, the 16-bit data sample is received most significant bit first, beginning at the bit slot defined by
the RTS and RCS control registers. The reception lasts for 16 consecutive bit slots.
SR selects between 8 kHz and 16 kHz sampling rates. However, FS remains constant at 8 kHz.
Therefore, in 16 kHz sampling mode, two data samples are transmitted to (or received from) the PCM
highway starting at the bit slot dictated by the time and clock slot registers. In 16 kHz mode, either two or
four adjacent 8-bit time slots are used for two compressed 8-bit data samples or two linear 16-bit data
samples, respectively. The 16 kHz mode is enabled by setting SR=1 followed by SEL16K=1.
When switching to 16 kHz sampling rate and if the Call Progress Monitor function is being used, the
Line-Side Device needs to be reconfigured. See Section 7.7.
PCM highway interfaces are designed such that a device can transmit and receive to other devices on the
PCM highway. For example, Codec A will use a time slot assignment for its transmit to the PCM highway
and Codec B will assign its receiver to the same time slot. The time slot assignment is such that if Codec
A wants to transmit its data sample to Codec B, then Codec A transmit time/clock slot value is identical to
the Codec B receive time/clock slot value.
The 73M1x66B uses the DX signal pin to transmit to the PCM highway and the DR signal pin to receive
from the PCM highway. Figure 22 illustrates a typical example.
DR
DR
DR
Codec A
Codec B
Codec N
DX
TSC
DX
TSC
DX
TSC
To System
PCM Highway
Figure 22: Example of PCM Highway Interconnect
Larger systems may use buffers to interconnect multiple segments of the PCM highway (across line cards
for instance). In the 73M1x66B, Control TSC is used to control the tri-state mode of the transmit side of
the PCM highway as shown in Figure 23. TSC is asserted (active low) for the duration of the time slot
during which the 73M1x66B is transmitting to the PCM highway.
Receive PCM Highway
From System
DR
DR
DR
Codec A
Codec B
Codec N
DX
TSC
DX
TSC
DX
TSC
TSC Tri-State Control
Transmit PCM Highway
To System
Figure 23: Example of PCM Highway Interconnect for Typical Large Systems
46
Rev. 1.6
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
