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2) Receiver
The receiver provides the following two functions:
1) Data reception
2) Collision detection
Fig. 16-29
1
Data reception
The 75115 is a dual-channel receiver containing two comparators.
One of the comparators is used to detect received data (RDI). The
data received from the line is applied to the negative input (pin 5)
of the comparator. The received data is also amplified by Q5,
integrated by R320 and C204, and voltage-divided by R34 and
VR1 before being applied to the positive input (pin 7) of the same
comparator, This assures reliable identification of "0" and "1" lev-
els even if the received data signal is distorted due to a long line
length.
The 75115 is a dual-channel receiver containing two comparators.
One of the comparators is used to detect received data (RDI). The
data received from the line is applied to the negative input (pin 5)
of the comparator. The received data is also amplified by Q5,
integrated by R320 and C204, and voltage-divided by R34 and
VR1 before being applied to the positive input (pin 7) of the same
comparator, This assures reliable identification of "0" and "1" lev-
els even if the received data signal is distorted due to a long line
length.
Note: If Transistor Q5 is replaced for servicing, the VR3 requires
readjustment. See the section for adjustment.
2
Collision detection
The other comparator in the 75115 is used for collision detection.
The SRN communication uses only a single transmission line, and
the transmission line is connected to each terminal. Only one pair
of terminals can communicate with each other over the transmis-
sion line at a time. If the transmission line is busy, other terminals
must wait to transmit until the line becomes available. The line
busy condition is monitored by the collision detector. The line sig-
nal is applied to the positive input (pin 9) of the comparator, while
the local send signal is applied to the negative input (pin 11) of the
same comparator, so that correct transmission can be monitored
by comparing the line signal with the transmission signal. If two
terminals attempt transmission at the same time, data collision will
occur on the line, which results in the line signal being different
from the local transmission signal. Detecting this difference, the
collision detector outputs a COL signal to indicate it to the CPU.
The other comparator in the 75115 is used for collision detection.
The SRN communication uses only a single transmission line, and
the transmission line is connected to each terminal. Only one pair
of terminals can communicate with each other over the transmis-
sion line at a time. If the transmission line is busy, other terminals
must wait to transmit until the line becomes available. The line
busy condition is monitored by the collision detector. The line sig-
nal is applied to the positive input (pin 9) of the comparator, while
the local send signal is applied to the negative input (pin 11) of the
same comparator, so that correct transmission can be monitored
by comparing the line signal with the transmission signal. If two
terminals attempt transmission at the same time, data collision will
occur on the line, which results in the line signal being different
from the local transmission signal. Detecting this difference, the
collision detector outputs a COL signal to indicate it to the CPU.
10. Collision detect circuit
The access system employs the carrier sense multiple access with
collision detect (CSMA/CD) with a BUS type topology. The access
system has no control station on the network and checks the space
area condition of the circuit according to the process is available.
Collision is detected sometimes due to the delay on the circuit or the
simulataneous data sending, but the collision is detected immediately
by the collision detect circuit and prevents the deterioration of the
transmission efficiency by providing the backoff process (binary expo-
nential backoff). The carrier sense is detected by the two stages of
the data packet and response packet to prevent the collision of the
response packet. This permits higher efficiency for heavy loads.
Collision detect circuit is located within the MB62H149 custom LSI.
collision detect (CSMA/CD) with a BUS type topology. The access
system has no control station on the network and checks the space
area condition of the circuit according to the process is available.
Collision is detected sometimes due to the delay on the circuit or the
simulataneous data sending, but the collision is detected immediately
by the collision detect circuit and prevents the deterioration of the
transmission efficiency by providing the backoff process (binary expo-
nential backoff). The carrier sense is detected by the two stages of
the data packet and response packet to prevent the collision of the
response packet. This permits higher efficiency for heavy loads.
Collision detect circuit is located within the MB62H149 custom LSI.
11. Carrier detect circuit
This circuit detects whether data is flowing on the transmission line. It
consists of a circuit which immediately senses a no data status on the
line.
consists of a circuit which immediately senses a no data status on the
line.
Fig. 30
When data is not on the line the circuit functions to sense an elapse of
the fixed time rate. The immediate sensing circuit is used for response
testing and the delayed sensing circuit is used for data testing.
This circuit is located within MB62H149 custom LSI.
the fixed time rate. The immediate sensing circuit is used for response
testing and the delayed sensing circuit is used for data testing.
This circuit is located within MB62H149 custom LSI.
+12V
+5V
Transmitter
LINE
GND
COL
RDI
14
15
13
9
11
R322
1.2K
Q5
R320 3.9K
R321
1K
1K
C204
3300P
R324
1.5K
VR3
2
1
7
8
+5V
12K
RTS
75115
3
4
R319
15K
+12V
Transmit data
5K
R323
MB62H149
75115
65
COL
15
LINE
– 73 –
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