Motorola MC68824 User Manual page 54

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Data in memory buffers organized with high order byte in lower address (Motorola and
IBM convention)
SWAP
=
1 - Intel Convention
D
c
B A
ODD (HIGHER) ADDRESS EVEN (LOWER) ADDRESS
SWAP
=
0 - Motorola Convention
D
c
B A
EVEN (LOWER) ADDRESS ODD (HIGHER) ADDRESS
In an 8-bit mode, this bit has no significance. Note that while the data organization of data
buffers and the frame header in the FD may be selected by this option, all other parameters,
pointers, and tables are organized according to the Motorola/IBM convention.
PS3 - Prescaler 3 Bit Mode
1 Prescaler of three bits for octet timers
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Prescaler of six bits for octet timers
The following octet variables, which are either parameters or statistics, are located in the
private area or in the initialization area of the initialization table and are subject to a prescaling
of three or six bits as set by the PS3 bit:
HLpriority_token_hold time Parameter
Last token_rotation_time Statistic
Token rotation time at start of access classes (0, 2, and 4) Statistic
Target token rotation time for access classes (0, 2, and 4) Parameter
Token rotation time at start of ring maintenance Statistic
Target token rotation time for ring maintenance Parameter
Ring maintenance timer initial value Parameter
The prescaling mechanism provides a resolution of 8 or 64 octets for all the values listed
above. The amount of prescaling must be chosen such that after prescaling, the parameters
will fit into 15 bits. Thus, if the largest target rotation time parameter or the expected token
rotation time is larger than (2
18 )
-1 octet times, the prescaler size must be six bits. When
rotation times are this large, the eight octet resolution is finer than needed, and the 64 octet
resolution is sufficient. A value of FFFF for anyone of the statistics listed above indicates an
overflow.
3.3.4 SET/CLEAR IN_RING DESIRED Command
This command is used to change the value of in_ring desired during normal operation. This
method of clearing, or setting, in_ring desired should be used rather than the SET MODE 2
command during normal operation. A description of the in_ring desired variable, which is an IEEE
802.4 boolean, is found in 3.3.2 SET MODE 2 Command. The coding for this command is CB or
CF and its format is:
Where:
1 Set In_Ring Desired
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Clear In_Ring Desired
MC68824 USER'S MANUAL
MOTOROLA
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