PM7385 FREEDM-84A672
DATA SHEET
PMC-1990114
ISSUE 6
84 LINK, 672 CHANNEL FRAME ENGINE AND DATA LINK MANAGER
WITH ANY-PHY PACKET INTERFACE
(device 0), it must be reselected before any further data is provided on the Rx
APPI.
At the end of the first 100 word packet transfer across the Rx APPI, the
FREEDM-84A672 automatically deselects and must be reselected before the
second two word packet is transferred. When the external controller samples
REOP high, it recognizes that the burst transfer has completed. Two RXCLK
cycles later, the external controller reselects FREEDM-84A672 device 0 by
setting RENB high and placing address 0 on the RXADDR[2:0] signals. When
the FREEDM-84A672 samples RENB low, it begins the next data transfer as
before.
Figure 18 – Receive APPI Timing (Optimal Reselection)
RXCLK
RXADDR[2:0]
RPA
Dev 0
NULL
Dev 7
Dev 0
NULL
CH 2
Dev 6
Dev 7
NULL
D1
NULL
D125
Dev 0
D126
NULL
D127
Dev 4
Dev 0
NULL
Dev 0
Dev 3
NULL
Dev 4
D128
RENB
Dev 0
RXDATA[15:0]
RVAL
D0
CH 2
RSX
REOP
RMOD
RERR
Figure 18 shows optimal bandwidth utilization across the Rx APPI.
With knowledge that the maximum burst data transfer (excluding channel
address prepend) is 256 bytes, i.e. 128 words, the external controller sets RENB
high when the 127th word (D126) is placed on RXDATA[15:0] in anticipation of the
end of a burst transfer. The FREEDM-84A672 completes the burst data transfer
and tristates the Rx APPI one RXCLK cycle after RENB is sampled high.
Because the burst data transfer is complete and RENB is immediately returned
low following selection, the FREEDM-84A672 immediately begins the next data
transfer following the single turn-around cycle.
The protocol dictates that at least one tristate turn-around cycle be inserted
between data transfers, even if the external controller is reselecting the same
FREEDM-84A672 device. In other words, Figure 18 shows the earliest possible
time that the external controller could have set RENB high to reselect FREEDM-
84A672 device 0.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
213
PMC [ PMC-SIERRA, INC ]
