mc68181 Freescale Semiconductor, Inc, mc68181 Datasheet - Page 38

• Manufacturer Part Number: mc68181
• Description: Signal Processor
• Manufacturer: Freescale Semiconductor, Inc

MC68181
FLEX Message Word Definitions
A-10
Symbol
M
N
K
C
R
F
1
12-bit Fragment Check Sum—This check sum is calculated by initializing the
Fragment Check Sum field (K) to 0 and calculating a sum over the information bits of
each code word in the message fragment (including control information and
termination characters/bits in the last fragment word). This sum requires that the
information bits of each word be broken into three groups: the first is the 8 bits
comprising i
third group comprises bits i
group. The binary sum is calculated over all code words in the fragment, the one’s
complement of the sum is determined, and the twelve LSBs of the result is placed into
the Fragment Check Sum field to be transmitted at the beginning of the fragment.
1-bit Message Continued Flag—When set to 1, this flag indicates fragments of this
message are to be expected in any or possibly all of the following frames until a
fragment with C = 0 is found. The longest message that fits into a frame is eighty-four
code words. Three alpha characters per word yields a maximum message of 252
characters in a frame, assuming no other traffic. Messages longer than this value must
be sent as several fragments.
2-bit Message Fragment Number—This is a modulo 3 message fragment number
that is incremented by 1 in successive message fragments. The initial fragment starts
at 11 and each following fragment is incremented by 1 modulo 3, (11, 00, 01, 10, 00, 01,
10, 00, etc.). The 11 state (after the initial fragment) is skipped in this process to avoid
confusion with the single fragment of a non-continued message. The final fragment is
indicated by the Message Continued Flag being reset to 0.
Message Number—When the system supports message retrieval the system
controller assigns message numbers (for each paging address separately) starting at 0
and progressing up to a maximum of 63 in consecutive order. The actual maximum
roll over number is defined in the pager code plug to accommodate values set in the
system infrastructure. When message numbers are not received in order, the
subscriber should assume a message has been missed. The subscriber or the pager
may determine the missing message number(s) allowing a request to be made for
retrieval. When a normal unnumbered numeric message is received (message
retrieval flag is equal to 0), it is not to be included in the missed message calculation.
This number is also used to identify fragments of the same message. Multiple
messages to the same address must have separate message numbers. An exception to
this rule is the header message tied to a transparent message, each with the same
message number.
Message Retrieval Flag—When this bit is set to 1, the pager expects to see messages
numbered in order (each address numbered separately). Detection of a missing
number indicates a missed message. A message received with R = 0 is allowed to be
out of order and not cause the pager to indicate that a message has been missed.
1-bit Mail Drop Flag—When set to 1, this bit indicates the message is to be stored in
a special area in memory. It automatically writes over existing data in that memory
space.
Table A-6 Hex/Binary Message Bit Definitions
0
MC68181 Technical Data Sheet
through i
Freescale Semiconductor, Inc.
For More Information On This Product,
7
, the second group comprises bits i
Go to: www.freescale.com
16
through i
Definition
20
. Bits i
0
, i
8
, and i
16
8
are the LSBs of each
through i
15
, and the
MOTOROLA