Previous Station Address; Last Token-Rotation-Time - Motorola MC68824 User Manual

low word of this address is stored in an internal TBC register while the middle and high words
are stored in the private area. Next station address may be accessed through the READ VALUE
command (see 3.5.2 READ VALUE for details).
Offset
00
02
I
MSB
D
c
2.1.2 Previous Station Address
B A
Next Station - High Word
Next Station - Middle Word
LSB
I
Previous station (PS) address is the 48-bit (or 16-bit) address of the previous station that passes
the token to this station. The low word of this address is stored in an internal TBC register with
the middle and high words stored in the private area. Previous station address is accessed through
the READ VALUE command.
Offset
04
06
I
MSB
D
c
B
2.1.3 HLPiority_ Token_Hold Time
A
Previous Station - High Word
Previous Station - Middle Word
LSB
I
The hLpriority_token_hold time can be from 0 to (2
16
)-1 octet times before prescaling (see 3.3.3
SET MODE 3 for details on scaling). If the priority option is used, the hLpriority_token_hold_time
is the maximum" amount of time the station may transmit data from the highest priority queue
(queue 6). If the priority option is not used, the hLpriority_token_hold_time determines the max-
imum amount of time the station can transmit before passing the token. The IEEE 802.4 standard
specifies the maximum value for this timer to be (2
16
)-1 octet times which therefore requires the
user to zero the upper three bits or the upper six bits of this word depending on the prescaling
factor used. However, the TBC does not check that this parameter is within the specified range
which allows the user to specify a timer with a maximum value of (2
22
)-1. This parameter must
be initialized by the host through the initialization table and may be altered or read via the SET/
READ VALUE command thereafter.
Offset
08
08
I
0
D
c
B A
o
I
0
I
0
I
0
I
0
2.1.4 Last Token_Rotation_ Time
HLPriority_Token_Hold Time (Prescaler of 3)
HLPriority_Token_Hold Time (Prescaler of 6)
Last token_rotation_time is the observed prescaled-octet time measured from the last time the
station had the token to when the station receives the token again, timed from token arrival to
token arrival. This statistic is updated every time the TBC receives the token. Last to-
ken_rotation_time can be accessed by the host via the READ VALUE command. The worst case
token_rotation_time is equal to the total of the token hold times for all the nodes on the network
plus the time it takes to pass the token between nodes. A value of zero indicates that the value
is not currently available and occurs, for example, when the token is not rotating.
Offset
OA
D
MC68824 USER'S MANUAL
c
B A
Last Token_Rotation_Time (Prescaled)
MOTOROLA
II