
DATA SHEET
PM7367 FREEDM-32P32
ISSUE 2
PMC-1991499
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE
284
13
FUNCTIONAL TIMING
13.1 Receive Link Input Timing
The timing relationship of the receive clock (RCLK[n]) and data (RD[n]) signals of
an unchannelised link is shown in Figure 22. The receive data is viewed as a
contiguous serial stream. There is no concept of time-slots in an unchannelised
link. Every eight bits are grouped together into a byte with arbitrary alignment.
The first bit received (B1 in Figure 22) is deemed the most significant bit of an
octet. The last bit received (B8) is deemed the least significant bit. Bits that are
to be processed by the FREEDM-32P32 are clocked in on the rising edge of
RCLK[n]. Bits that should be ignored (X in Figure 22) are squelched by holding
RCLK[n] quiescent. In Figure 22, the quiescent period is shown to be a low level
on RCLK[n]. A high level, effected by extending the high phase of the previous
valid bit, is also acceptable. Selection of bits for processing is arbitrary and is
not subject to any byte alignment nor frame boundary considerations.
Figure 22 – Unchannelised Receive Link Timing
RCLK[n]
RD[n]
B1 B2 B3 B4 X B5 X X
X B6 B7 B8 B1 X
The timing relationship of the receive clock (RCLK[n]) and data (RD[n]) signals of
a channelised T1 link is shown in Figure 23. The receive data stream is a T1
frame with a single framing bit (F in Figure 23) followed by octet bound time-slots
1 to 24. RCLK[n] is held quiescent during the framing bit. The RD[n] data bit (B1
of TS1) clocked in by the first rising edge of RCLK[n] after the framing bit is the
most significant bit of time-slot 1. The RD[n] bit (B8 of TS24) clocked in by the
last rising edge of RCLK[n] before the framing bit is the least significant bit of
time-slot 24. In Figure 23, the quiescent period is shown to be a low level on
RCLK[n]. A high level, effected by extending the high phase of bit B8 of time-slot
TS24, is equally acceptable. In channelised T1 mode, RCLK[n] can only be
gapped during the framing bit. It must be active continuously at 1.544 MHz
during all time-slot bits. Time-slots can be ignored by setting the PROV bit in the
corresponding word of the receive channel provision RAM in the RCAS block to
low.