MT91L60/61
Preliminary Information
SSI Mode
For asynchronous operation Dout and Din are as
defined for synchronous operation except that the
allowed output jitter on Dout is larger. This is due to
the resynchronization circuitry activity and will not
affect operation since the bit cell period at 128 kb/s
and 256 kb/s is relatively large. There is a one frame
delay through the FDI circuit for asynchronous
operation. Refer to the specifications of Figures 12
& 13 for both synchronous and asynchronous SSI
timing.
The SSI BUS consists of input and output serial data
streams named Din and Dout respectively, a Clock
input signal (CLOCKin), and a framing strobe input
(STB). The frame strobe must be synchronous with,
and eight cycles of, the bit clock. A 4.096 MHz
master clock is also required for SSI operation if the
bit clock is less than 512 kHz. The timing
requirements for SSI are shown in Figures 12 & 13.
PWRST/Software Reset (Rst)
In SSI mode the MT91L60/61 supports only
B-Channel operation. The internal C and D Channel
registers used in ST-BUS mode are not functional for
SSI operation. The control bits TxBSel and RxBSel,
as described in the ST-BUS section, are ignored
since the B-Channel timeslot is defined by the input
STB strobe. Hence, in SSI mode transmit and
receive B-Channel data are always in the channel
defined by the STB input.
While the MT91L60/61 is held in PWRST no device
control or functionality is possible. While in software
reset (Rst=1, address 03h) only the microport is
functional. Software reset can only be removed by
writing the Rst bit low or by performing a hardware
PWRST. While the Rst bit is high, the other bits in
Control Register 1 are held low and cannot be
reprogrammed. Therefore to modify Control Register
1 the Rst bit must first be written low, followed by a
2nd write operation which writes the desired data.
This avoids a race condition between clearing the
reset bit and the writing of the other bits in Control
Register 1.
The data strobe input STB determines the 8-bit
timeslot used by the device for both transmit and
receive data. This is an active high signal with an 8
kHz repetition rate.
The MT91L61 provides a
delayed strobe pulse which occurs after the initial
strobe goes low and is held high for the duration of 8
pcm bits.
After a Power-up reset (PWRST) or software reset
(Rst) all control bits assume their "Power Reset
Value" default states; µ-Law coding, 0 dB Rx and
6dB Tx gains and the device powered up in SSI
mode 2048 kb/s operation with Dout tri-stated while
there is no strobe active on STB. If a valid strobe is
supplied to STB, then Dout will be active, during the
defined channel.
SSI operation is separated into two categories based
upon the data rate of the available bit clock. If the bit
clock is 512 kHz or greater then it is used directly by
the internal MT91L60/61 functions allowing
synchronous operation. If the available bit clock is
128 kHz or 256 kHz, then a 4096 kHz master clock is
required to derive clocks for the internal MT91L60/61
functions.
To attain complete power-down from a normal
operating condition, write PDFDI = 1 and PDDR = 1
(Control Register 1, address 03h) or set the PWRST
pin low.
Applications where Bit Clock (BCL) is below 512 kHz
are designated as asynchronous. The MT91L60/61
will re-align its internal clocks to allow operation
when the external master and bit clocks are
asynchronous. Control bits CSL2, CSL1 and CSL0 in
Control Register 2 (address 04h) are used to
program the bit rates.
For synchronous operation data is sampled, from
Din, on the falling edge of BCL during the time slot
defined by the STB input. Data is made available, on
Dout, on the rising edge of BCL during the time slot
defined by the STB input. Dout is tri-stated at all
times when STB is not true. If STB is valid and
PDDR is set, then quiet code will be transmitted on
Dout during the valid strobe period. There is no
frame delay through the FDI circuit for synchronous
operation.
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MITEL [ MITEL NETWORKS CORPORATION ]
