![](http://datasheet.mmic.net.cn/330000/PM7367-PI_datasheet_16444408/PM7367-PI_46.png)
DATA SHEET
PM7367 FREEDM-32P32
ISSUE 2
PMC-1991499
FRAME ENGINE AND DATA LINK MANAGER
8.2.1 Line Interface
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE
32
There are 32 identical line interface blocks in the RCAS. Each line interface
contains a bit counter, an 8-bit shift register and a holding register, that, together,
perform serial to parallel conversion. Whenever the holding register is updated,
a request for service is sent to the priority encoder block. When acknowledged
by the priority encoder, the line interface would respond with the data residing in
the holding register.
To support channelised links, each line interface block contains a time-slot
counter and a clock activity monitor. The time-slot counter is incremented each
time the holding register is updated. The clock activity monitor is a counter that
increments at the system clock (SYSCLK) rate and is cleared by a rising edge of
the receive clock (RCLK[n]). A framing bit (T1) or framing byte (E1) is detected
when the counter reaches a programmable threshold. In which case, the bit and
time-slot counters are initialised to indicate that the next bit is the most significant
bit of the first time-slot. For unchannelised links, the time-slot counter and the
clock activity monitor are held reset.
8.2.2 Priority Encoder
The priority encoder monitors the line interfaces for requests and synchronises
them to the SYSCLK timing domain. Requests are serviced on a fixed priority
scheme where highest to lowest priority is assigned from the line interface
attached to RD[0] to that attached to RD[31]. Thus, simultaneous requests from
RD[m] will be serviced ahead of RD[n], if m < n. When there are no pending
requests, the priority encoder generates an idle cycle. In addition, once every
fourth SYSCLK cycle, the priority encoder inserts a null cycle where no requests
are serviced. This cycle is used by the channel assigner downstream for host
microprocessor accesses to the provisioning RAMs.
8.2.3 Channel Assigner
The channel assigner block determines the channel number of the data byte
currently being processed. The block contains a 1024 word channel provision
RAM. The address of the RAM is constructed from concatenating the link
number and the time-slot number of the current data byte. The fields of each
RAM word include the channel number and a time-slot enable flag. The time-slot
enable flag labels the current time-slot as belonging to the channel indicted by
the channel number field.