Preliminary Information
125
µs
F0i
MT9196
DSTi,
DSTo
CHANNEL 0
D-channel
LSB first
for D-
Channel
CHANNEL 1
C-channel
CHANNEL 2
B1-channel
CHANNEL 3
B2-channel
CHANNELS 4-31
Not Used
MSB first for C, B1- & B2-
Channels
Figure 7 - ST-BUS Channel Assignment
between the IDPC and the microcontroller. At the
end of the two-byte transfer CS is brought high again
to terminate the session. The rising edge of CS will
tri-state the output driver of DATA1 which will remain
tri-stated as long as CS is high.
Intel processors utilize least significant bit first
transmission while Motorola/National processors
employ most significant bit first transmission. The
IDPC microport automatically accommodates these
two schemes for normal data bytes. However, to
ensure timely decoding of the R/W and address
information, the Command/Address byte is defined
differently for Intel operation than it is for Motorola/
National operation. Refer to the relative timing
diagrams of Figures 5 and 6.
Receive data is sampled on the rising edge of SCLK
while transmit data is made available concurrent with
the falling edge of SCLK.
Detailed microport timing is shown in Figure 15.
Flexible Digital Interface
A serial link is required to transport data between the
IDPC and an external digital transmission device.
IDPC utilizes the ST-BUS architecture defined by
Mitel Semiconductor but also supports a strobed
data interface found on many standard CODEC
devices. This interface is commonly referred to as
Synchronous Serial Interface (SSI). The combination
of ST-BUS and SSI provides a Flexible Digital
Interface (FDI) capable of supporting all Mitel basic
rate transmission devices as well as many other
2B + D transceivers.
The required mode of operation is selected via the
ST-BUS/SSI control bit (FDI Control Register,
address 10h). Pin definitions alter dependent upon
the operational mode selected, as described in the
following subsections as well as in the Pin
Description tables.
Quiet Code
The FDI can be made to send quiet code to the
decoder and receive filter path by setting the
RxMUTE bit high. Likewise, the FDI will send quiet
code in the transmit (DSTo) path when the TxMUTE
bit is high. Both of these control bits reside in Control
Register 1 at address 0Eh. When either of these bits
are low their respective paths function normally. The
-Zero entry of Table 1 is used for the quiet code
definition.
ST-BUS Mode
The ST-BUS consists of output (DSTo) and input
(DSTi) serial data streams, in FDI these are named
Dout and Din respectively, a synchronous clock input
signal CLOCKin (C4i), and a framing pulse input
(F0i). These signals are direct connections to the
corresponding pins of Mitel basic rate devices. Note
that in ST-BUS mode the XSTL2 pin is not used. The
CSL1 and CSL0 bits, as described in the SSI Mode
section, are also ignored since the data rate is fixed
for ST-BUS operation. However, the Asynch/Synch
bit must be set to logic “0” for ST-BUS operation.
The data streams operate at 2048 kb/s and are Time
Division Multiplexed into 32 identical channels of 64
kb/s bandwidth. A frame pulse (a 244 nSec low going
pulse) is used to parse the continuous serial data
streams into the 32 channel TDM frames. Each
frame has a 125 µSecond period translating into an 8
kHz frame rate. A valid frame begins when F0i is
logic low coincident with a falling edge of C4i. Refer
to Figure 12 for detailed ST-BUS timing. C4i has a
frequency (4096 kHz) which is twice the data rate.
This clock is used to sample the data at the 3/4 bit-
cell position on DSTi and to make data available on
DSTo at the start of the bit-cell. C4i is also used to
clock the IDPC internal functions (i.e., Filter/CODEC,
Digital gain and tone generation) and to provide the
channel timing requirements.
The IDPC uses only the first four channels of the 32
channel frame. These channels are always defined,
7-137
MITEL [ MITEL NETWORKS CORPORATION ]
