
RELEASED
DATA SHEET
PM7366 FREEDM-8
ISSUE 4
PMC-1970930
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
248
14
FUNCTIONAL TIMING
14.1 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-8 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.
Figure 23 – Channelised T1 Receive Link Timing
RCLK[n]
RD[n]
B7 B8 F B1 B2 B3 B4 B5 B6 B7 B8 B1 B2 B3
TS 24
TS 1
TS 2