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2.1.23 RWR Maximum Retry Limit
The request with response (RWR) maximum retry limit sets an upper bound to the number of
times the T8C will attempt to transmit a RWR frame. A retry is performed if an underrun occurs
or if no response is received from the destination address. This parameter is initialized by the
II
host through the initialization table and may be altered or read via the SET/READ VALUE command
thereafter. In the IEEE 802.4 standard, the maximum RWR number of retries value is seven. The
maximum value that the T8C will support is 255.
Offset
6E
1
0
1
0
2.1.24 Slot Time
o
c
B
A
01 0 10101 0
o
o
1
RWR Maximum Retry Limit
Slot time is the worst case time any station must wait for a response from another station. This
parameter must be uniform throughout the network. It is equal to the amount of time for the
slowest station on the bus to respond to MAC control frames. Slot time is measured in octet
times, has a maximum value of (2
13 )
-1 and is defined by the equation below:
SLOT TIME
=
Integer ((2·Transmission_Path_Delay)
+
(((2·Station_Delay)
+
Safety_Margin)/MAC_SymboL Time)/8)
The transmission path delay is the worst case delay which transmissions experience going through
the physical medium from a transmitting station to a receiving station. The station delay is the
amount of time from the receipt of the end delimiter at the receiving station's physical medium
interface until the impression of the first bit of the preamble on the physical medium by the
receiving station's transmittter. The safety margin in the time interval is no less than one MAC
symbol time. MAC symbols are defined as the smallest unit of information exchanged between
the MAC sublayer entities. MAC symbol time is the time required to send a single MAC symbol
and is therefore the inverse of the network data rate.
Offset
70
F E D
C
1
0
1
0 1 0
1
2.1.25 This Station Address
B
A
4
o
Slot Time (In Octets)
This station address (TS) is a 48-bit or 16-bit address which must be an even integer since an
odd address represents a group address. It contains the address used by the TBC to accept or
reject MAC frames. This parameter is initialized by the host through the initialization table and
may be read via the READ VALUE command thereafter. The middle and high words should be
zero if the address length is 16 bits. Note that this parameter is stored following the IEEE format.
Offset
72
74
76
o
C
B
A
This Station Address - low Word
This Station Address - Middle Word
This Station Address - High Word
2.1.26 Manufacturer Product Revision and 802.4 Standard Revision Number
lSB
I
The value of this parameter is "0402 hex" for T8C mask set 2A60S and "0502 hex" for T8C mask
set 18598. It is stored at offset 78. The '4' or '5' is an indication of the manufacturer product
MC68824 USER'S MANUAL
MOTOROLA
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