PM4341AT1XC
DATA SHEET
PMC-900602
ISSUE 7
T1 FRAMER/TRANSCEIVER
Register 0EH:T1XC Phase Status Word (LSB)
Bit
Type
Function
Default
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
R
R
R
R
R
R
R
R
PSB[7]
PSB[6]
PSB[5]
PSB[4]
PSB[3]
PSB[2]
PSB[1]
PSB[0]
X
X
X
X
X
X
X
X
This register contains the least significant byte, PSB[7:0], of the 9-bit phase
status word.The 9-bit phase status word indicates the relative phase difference
between the received DS-1 line timing (available on RCLKO) and a system timing
which uses either a 2.048MHz backplane (input on BRCLK, with BRX2M=1 in
Reg. 00H) or a 1.544MHz backplane (input on BRCLK, with BRX2M=0). By
utilizing the value of the phase status word, the system timing can be locked to
the receive line timing via an external software controlled phase-locked-loop.
The least significant 8 bits contained in this register indicate a count value (either
0-255 for BRX2M=1 or 0-192 for BRX2M=0) of the number of system backplane
clock cycles between successive 125µs frame pulses.The most significant 5 bits
(PSB[7:3]) represent a channel number (0-31 for BRX2M=1 or 0-23 for
BRX2M=0) and the least significant 3 bits (PSB[2:0]) represent the bit number
within the channel (0-7). The count value corresponds to the location within the
system frame where the receive line-timed frame pulse occurred. If the received
line clock frequency is higher on average than the system clock frequency, the
phase status word value will be seen to decrease during successive register
reads. If the received line clock frequency is lower on average than the system
clock frequency, the phase status word value will be seen to increase during
successive register reads.
The 9th bit of the Phase Status Word indicates the "frame count" and will toggle
when two successive 8-bit counter values straddle a frame boundary.The
PSB[8] bit will toggle when the bit and channel count indicated by PSB[7:0]
exceeds channel 31, bit 7 (when BRX2M=1; or channel 23, bit 7 when
BRX2M=0) or the count goes below channel 0, bit 0. This is determined by
comparing the PSB[7:5] bits of the current phase status word value to those of
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
94
PMC [ PMC-SIERRA, INC ]
