Cermetek Microelectronics, Inc.
CH1788 Surface Mount PLCC 2400bps Modem
2006 Cermetek Microelectronics, Inc.
Page 5
Document No. 607-0018 Revision A6 (01/06)
Figure 2. CH1788 Pin Configuration. See Table 2 for detailed Pin Descriptions.
Table 2. CH1788 Pin Descriptions.
PIN NAME TYPE
FUNCTION
1
A1
O
Optional Input.
Active high.
Used when implementing the 911 Priority Pick-Up
circuit or the Line In Use circuit.
2
OH
O
Off-Hook.
Active low. OH Indicates when the CH1788 is Off-Hook. Used in Line
In Use, 911 Priority Pick-Up applications and for Audio Control.
3
RTS
I
Request To Send
. Active low. Used for optional flow control. Used in conjunction
with the Clear to Send (CTS) pin as a handshaking signal. See the details of
register S90.
4
RI
O
Ring Indication.
Active low. For each occurrence of a valid ring signal, this pin will
pulse low for 70 ms. This output signal follows the frequency of the ringing signal
and is typically in the 20 to 40 Hz range with a cadence of 2 seconds on with 4
seconds off.
5
CTS
O
Clear to send.
Active low. Used for optional flow control. Used in conjunction with
the Request To Send (RTS) pin as a handshaking signal.
6
DSR
O
Data Set Ready.
Active low. A low indicates that handshaking with the remote
modem is in progress and/or the carrier of the remote modem has been detected
and a valid connection is imminent as measured by DCD being active. This feature
is enabled with the
N
command.
7
DCD
O
Data Carrier Detect.
Active low. This output must be enabled with the
ATC1
command. When enabled, it will become active when both the originated and
answering modems are connected and a data carrier has been detected.
NOTE: 1. All unused pins should be left unconnected when not required in a specific application,
unless specifically directed otherwise.
2. See DC characteristics before attempting to drive an LED directly from the output of any pin.
Used for LIU/911/Audio Control
CH1788
Top View
A1
OH
RTS
RI
CTS
DSR
DCD
DTR
A2
TXD
RST
RXD
GND
V
CC
S2
S1
V-
V+
TIP
RING
1
2
3
4
5
6
7
8
15
14
13
12
22
21
20
19
9
10
11
18
DTE Signal
Power Input +5V
DTE Signal
Optional S1/S2 Audio
Monitor/Tone/Voice
V+/V- Optional
CID Input
Telephone Line
Input
High Voltage Section
Used for LIU/911/General IO
DTE Signal
DTE Signal
DTE Signal
DTE Signal
DTE Signal
DTE Signal
Used for LIU/Detection
Optional High Reset Input
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