ZL38001 Data Sheet
14
Zarlink Semiconductor Inc.
3.0 PCM Data I/O
The PCM data transfer for the ZL38001 is provided through two PCM ports. One port consists of Rin and Sout pins
while the second port consists of Sin and Rout pins. The data are transferred through these ports according to
either ST-BUS, GCI or SSI conventions and the device automatically detects the correct convention. The device
determines the convention by monitoring the signal applied to the F0i
pin. When a valid ST-BUS (active low) frame
pulse is applied to the F0i
pin, the ZL38001 will assume ST-BUS operation. When a valid GCI (active high) frame
pulse is applied to the F0i
pin, the device will assume GCI operation. If F0i is tied continuously to Vss, the device
will assume SSI operation. Figures 11 to 13 show timing diagrams of these 3 PCM-interface operation conventions.
3.1 ST-BUS and GCI Operation
The ST-BUS PCM interface conforms to Zarlink’s ST-BUS standard with an active-low frame pulse. Input data is
clocked in by the rising edge of the bit clock (C4i
) three-quarters of the way into the bitcell and output data bit
boundaries (Rout, Sout) occur every second falling edge of the bit clock (see Figure 11.) The GCI PCM interface
corresponds to the GCI standard commonly used in Europe with an active-high frame pulse. Input data is clocked in
by the falling edge of the bit clock (C4i
) three-quarters of the way into the bitcell and output data bit boundaries
(Rout, Sout) occur every second rising edge of the bit clock (see Figure 12.)
Either of these interfaces (STBUS or GCI) can be used to transport 8 bit companded PCM data (using one timeslot)
or 16 bit 2’s complement linear PCM data (using two timeslots). The MD1/ENA1 pins select the timeslot on the
Rin/Sout port while the MD2/ENA2 pin selects the timeslot on the Sin/Rout port, as in Table 3. Figures 3 to 6
illustrate the timeslot allocation for each of these four modes.
Figure 3 - ST-BUS and GCI 8-Bit Companded PCM I/O on Timeslot 0 (Mode 1)
C4i
F0i (ST-BUS)
Sin
Rout
Rin
Sout
76543
210
76543
210
76543
210
76543
210
outputs = High impedance
inputs = don’t care
In ST-BUS/GCI Mode 1, echo canceller I/O channels are assigned to ST-BUS/GCI timeslot 0. Note that the user can configure PORT1
and PORT2 into different modes.
PORT1
PORT2
01 2 34
B
F0i (GCI)
start of frame (stbus & GCI)
EC
EC
