Sharp ER-A57R1 Service Manual page 56

3) Pin Configuration (top view)
VSS 1
RTS 2
RXD 3
RXC 4
TXC 5
TXD 6
IRQ 7
RESET 8
CS 9
RS0 10
RS1 11
R/W 12
E 13
VCC 14
7. Modulator/Demodulatro circuit
Phase encoding (PE) modulation is used for SRN communications.
The PE modulation has a changing point in the signal at the center of
the bit, the timing signal is regenerated from this signal, making the
modulation and demodulation simpler by providing continuous signals
for the DC conponents.
Data 0 1 1
NRZ
PE
Fig. 27 PE Modulation
Serial send data applied from the ADLC to TXD (pin 72) of the
MB62H149 and the TXC synchronization signal is subject to PE
modulation. The resulting signal is output through TDI (pin 67) of the
MB62H149 to the transmission driver.
Received data is applied from the receiver to RDI (pin 66) of the
MB62H149, where it is demodulated into serial receive data and
synchronization clock. They are output to the ADLC through RXS (pin
70) and RXC (pin 69), respectively.
The modulator and demodulator are located within the MB62H149.
8. Transmitter and Receiver Circuits
1) Transmitter
The modulated send data output through TDI (pin 67) of the
MB62H149 is controlled by the RTS (Request to Send) signal
transferred from the ADLC during transmission.
The TDI is NAND'ed with RTS, so that data transmission is disabled
when the RTS is high.
RTS is Low state during transmission and Transistor Q2 is turned ON.
When transmitting data "1", the output at pin 12 of the NAND gate
(IC7) is set Low. (the RTS is Low) Since pin 11
28 CTS
27 DCD
26 DTR/LOC
25 FD
24 TDSR
23 RDSR
22 D0
21 D1
20 D2
19 D3
18 D4
17 D5
16 D6
15 D7
Fig. 26
0 0 1 0 1
of the following transistor (IC7) is set Low, it is turned off.
When hte RTS is set Low, transistor Q1 turned on through an inverter,
which applies a bese current to Q2, turnit it on. When Q2 and pins 10
and 9 of IC7 are turned on, the output transistors IC7 (pins 6 and 5)
are turned on. Since the output trasistors are common-emitter circuit,
data "1" is obtained at LINE.
+12V
74HC04
R22
RTS 4
560
1
13
7
TDI
SN75450 BN
RTS
TDI
2) Receiver
The receiver provides the following two functions:
1) Data reception
2) Collision detection
RTS
75115 13
14
15
COL
2
1
RDI
3
+5V
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 Q3,
integrated by R15 and C32, and voltage-divided by R17 and VR1
before being applied to the positive input (pin 7) of the same
comparator, This assures reliable identification of "0" and "1"
levels even if the received data signal is distorted due to a lond
line length.
Note: If Transistor Q1 is replaced for servicing, the VR1 requires
readjustment. See the section for adjustment.
4 ™ 13
R20 Q2
R1
820
15
R3
R10
1K
5
220
4
Q1
6
10
R24
11
12
IC7
220
9
R25
470
+5V
Fig. 28
Transmit data
+12V
R16
1K
Q3 R23
R15 3.9K
1.2K
C32 3300P
VR1
R17
20K 1.5K
9
11
+5V
7
12K
8
4
R28
15K
Fig. 16-29
IC7
SN75450BN
LINE
GND
Transmitter
+12V
LINE
GND