Radio Shack TRS-80 PT-210 Service Manual page 15

CN2
I
T
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~ T X D
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BUFFER
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MODULATOR
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I
I
CONTROL
UNIT
CN3
Figure 1 1. Modem Logic Block Diagram
l -
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D S R
Names used in the modem logic are described below.
DSR (Data Set Ready): This signal indicates that the modem is in the status that permits operation in
the case where exchange of data is made between a modem and its control unit. This signal becomes
"L" level about 2-
4 seconds after input of data to MIC IN, and operation is enabled.
RxD (Required Data): Receives data signals transmitted from the modem and transfers them to the con-
trol side.
TxD (Transmitted Data): Transmits data signals
-
data signals produced from the control side are
transmitted to the modem.
INH (Inhibit): Signal for discontinuing transmission of data. Transmission is made while this input is at
level
"L".
MIC IN (Microphone Input Data):" The following analog frequencies are received from the telephone
handset.
Mark: 2,225
Â
5 Hz
Space: 2,025
Â
5 Hz
SP OUT (Speaker Output Data): The following analog frequencies are transmitted to the telephone
handset.
Mark: 1,270 & 5 Hz
Space: 1,070
Â
5 Hz
DEMODULATOR
1
RxD
I
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I
BANDPASS.
FILTER
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