Zilog Z16C30 - Manual (Page 86)

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Z16C30 USC ®
U SER ' S M ANUAL Z ILOG
UM97USC0100
CMR7-4 Address/Control Processing
xx00 The Receiver doesn’t handle the Address or Control
field. It simply divides all the data in all received
frames into characters per RxLength and places it
in the RxFIFO.
xx01 The Receiver checks the first 8 bits of each frame
as an address. If they are all ones or if they match
the contents of the LSByte of the Receive Sync
Register RSR7-0, the Receiver receives the frame
into the RxFIFO, otherwise it ignores the frame
through the next Flag. After placing the first 16 bits
of the frame in the FIFO as two 8-bit bytes, it
divides the rest of the frame into characters per
RxLength.
x010 The Receiver checks an 8-bit address as described
above. If these bits are all ones or if they match
RSR7-0, the Receiver places the first 24 bits of the
frame in the RxFIFO as 3 8-bit bytes, before
shifting to dividing characters according to
RxLength.
x110 The Receiver checks an 8-bit address as described
above. If these bits are all ones or if they match
RSR7-0, the Receiver places the first 32 bits of the
frame in the RxFIFO as 4 8-bit bytes, before
shifting to dividing characters according to
RxLength.
0011 The Receiver processes an Extended Address at
the start of each frame. First it checks the first 8 bits
of the frame as described above. If these bits are
all ones or if they match RSR7-0, as the Receiver
places each 8 bits of the address into the RxFIFO,
it checks the LSBit of the 8. If the LSBit is 0, it goes
on to put the next 8 bits into the RxFIFO as part of
the address as well, through an address byte that
has its LSBit 1. Then, the Receiver places the next
16 bits of the frame into the RxFIFO as two 8-bit
bytes, before shifting to dividing characters
according to RxLength.
0111 The Receiver processes an Extended Address as
described for 0011. If the first 8 bits of the address
are all ones or if they match RSR7-0, the Receiver
places the 24 bits after the extended address into
the RxFIFO as 3 8-bit bytes, before shifting to
dividing characters per RxLength.
CMR7-4 Address/Control Processing
1011 The Receiver processes an Extended Address as
described for 0011, and then an “Extended Con-
trol field”. If the first 8 bits of the address are all
ones or if they match RSR 7-0, the Receiver places
the next 8 bits after the extended address in the
RxFIFO without examination. Then, as it stores
each subsequent 8 bits in the RxFIFO, the Re-
ceiver checks the MSBit of the 8. If the MSBit is 1,
it continues to receive more 8-bit bytes, through
one that has its MSBit 0. Thereafter the Receiver
places one more 8-bit byte into the RxFIFO, before
shifting to dividing characters per RxLength.
1111 This mode differs from that described above for
1011 only in that the Receiver places the 16 bits
after the extended address in the RxFIFO without
examination, before starting to check MSBits for
the end of the “extended Control field”.
Note that even though the Receiver can scan through an
Extended Address, it will still only match its first byte. Note
also that it matches RSR0 against the first bit received, and
RSR7 against the last bit, regardless of whether software
has written a “Select Serial Data MSB First” command to
RTCmd (CCAR15-11).
If the RxSubMode field specifies some degree of Address
and Control checking, that is, if it’s not xx00, and a frame
ends before the end of the Address and possibly the
Control field specified by the RxSubMode value, the Re-
ceiver sets a Short Frame bit in the status for the last
character of the frame. This bit migrates through the
RxFIFO with the last character, eventually appearing as
the ShortF/CVType bit in the Receive Command/Status
register (RCSR8). Note that this bit can represent the
status at the time that an RxBound character was read from
the RxFIFO, or the status of the oldest 1 or 2 characters that
are still in the RxFIFO, as described in a later section,
'Status Reporting'. Note, however, that this length check-
ing doesn’t report a problem if a frame ends within a CRC
that follows an address and control field.
If RxLength (RMR4-2) is 000, specifying 8 bits per charac-
ter, all RxSubMode (CMR7-4) values except xx00 are
equivalent aside from short-frame checking.
UM009402-0201