BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
340
Section 10: Serial Interfaces
Document
1250_1125-UM100CB-R
The enable signal is level sensitive when used to enable the data. In transparent mode (see
Section: “Operation in Transparent Mode” on page 349
) the enable signal is used to frame the data, this can
be selected as being edge (inactive to active) or level based, but only the edge based framing is likely to be
useful.
RSTROBE is not used when the interface is used for an external enable. It is best to configure the pin as a
GPIO. If the pin is configured as RSTROBE it will remain deasserted.
Input Using the Internal Sequencer
An internal sequencer can be used to qualify received data bits. A user-configured table is used to generate
the internal enable signal and an optional external strobe signal. An external framing pulse provided on the
RIN pin is used to synchronize traversal of the table with the data stream. The table consists of up to 16 entries,
each with the format shown in
.
Each entry controls the behavior of the line interface for a number of bit times equal to Count+1 if Bit/Byte is
0, or to 8*(Count+1) if Bit/Byte is 1. During those bit times, DIN is sampled and processed on each clock edge
if Enable is 1; DIN is ignored and no data is sent to the protocol engine if Enable is 0. If the RSTROBE pin is
enabled then it will be driven with the value of Strobe bit in the entry.
The synchronization pulse on RIN is latched on the same clock edge as the data on DIN. The synchronization
pulse is delayed by 0, 1, 2 or 3 clocks. The edge_det bit in the
ser_mode
register selects either the active level
or the inactive to active edge of the delayed pulse as the start signal for the sequencer. If the sequencer is
currently idle it will reset to map table entry zero when started, and the enable bit in that entry becomes
effective immediately. Table entries are thereafter processed in order until encountering an entry with the Last
indicator set.
After the last entry of the table is processed, the line interface unit waits for the next assertion of delayed RIN
before it restarts with entry 0. During any interval between the end of the table and reassertion of RIN, DIN is
not sampled.
Once the table scan has started the start signal is ignored. If an active level or edge is detected on the delayed
RIN signal it will be flagged as an rx_sync_error in the
ser_status
register and it will not affect the sequencer.
(This may not be an error on some interfaces, for example if the sync is marked as level sensitive but lasts
more than one cycle.)
Table 225: Sequencer Table Entries
Bits
Name
Description
0
Last
Indicates current entry is the last entry of the table.
1
Bit/Byte 0:
Bit
1: Byte.
5:2
Count
One less than the number of bits/bytes controlled by this entry
6
Enable
Enables reception of the current data bit.
0: Disable
1: Enable
7
Strobe
Selects the value put on the external strobe pin while this entry is in use. The
ser_mode
register
is used to select if the strobe is active high or low.
0: Deassert
1: Assert
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