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ISAC-SX
PEB 3086
Description of Functional Blocks
Data Sheet
139
2003-01-30
The total length of the frame is contained in the RBCHx and RBCLx registers which
contain a 12 bit number (RBC11...0), so frames up to 4095 byte length can be counted.
If a frame is longer than 4095 bytes, the RBCH.OV (overflow) bit will be set. The least
significant bits of RBCLx contain the number of valid bytes in the last data block indicated
by RMEx (length of last data block
selected block size).
Table 18
shows which RBC
bits contain the number of bytes in the last data block or number of complete data blocks
respectively. If the number of bytes in the last data block is ’0’ the length of the last
received block is equal to the block size.
The transfer block size (EXMx.RFBS) is 32 bytes for D-channel and 16 bytes for B-
channel by default. If it is necessary to react to an incoming frame within the first few
bytes the microcontroller can set the RFIFOx block size to a smaller value. Each time a
CMDRx.RMC or CMDRx.RRES command is issued, the RFIFOx access controller sets
its block size to the value specified in EXMR.RFBS, so the microcontroller has to write
the new value for RFBS before the RMC command. When setting an initial value for
RFBS before the first HDLC activities, a RRES command must be issued afterwards.
The RFIFOx can hold any number of frames fitting in the 64 bytes (D-channel)/128 bytes
(B-channel). At the end of a frame, the RSTAx byte is always appended.
All generated interrupts are inserted together with all additional information into a wait
line to be individually passed to the host. For example if several data blocks have been
received to be read by the host and the host acknowledges the current block, a new RPF
or RME interrupt from the wait line is immediately generated to indicate new data.
Table 18
EXMD1.RFBS
bits
(D-channel)
Receive Byte Count with RBC11...0 in the RBCHx/RBCLx Registers
EXMB.RFBS
bit
(B-channel)
data blocks in
--
32 byte
RBC11...5
’0’
16 byte
RBC11...4
’1’
8 byte
RBC11...3
--
4 byte
RBC11...2
Selected
block size
Number of
complete
bytes in the last
data block in
RBC4...0
RBC3...0
RBC2...0
RBC1...0
’00’
’01’
’10’
’11’