Serial Link Electrical Interface - Multitech MMCModem MTMMC-G-F4 Developer's Manual

Serial Link Electrical Interface

A serial link interface is available complying with V24 protocol signaling but not with V28
(electrical interface) due to a 2.8 Volts interface. TX, RTS and DTR can be either 5V or 3V.
Data signals are Hi = Mark. Controls signals are Hi = Off.
The signals are Tx data (CT103/TX), Rx data (CT104/RX), Request To Send (CT105/RTS),
Clear To Send (CT106/CTS), Data Terminal Ready (CT108-2/DTR), Data Carrier Detect
(CT109/DCD), Ring Indicator (CT125/RI), and Data Set Ready (CT107/DSR).
Serial Link Pin Description
Signal
CT103 / TX
CT104 / RX
CT105 / RTS
CT106 / CTS
CT107 / DSR
CT108-2 / DTR
CT109 / DCD
CT125 / RI
* See "Operating Conditions" in the section on the 50-pin Connector Description.
Level Shifter Application for the Serial Link
Modem
Vcc
Multi-Tech Systems, Inc. MMCModem GPRS Developer's Guide (S000445D)
Pin # I/O
25 I
28 O
30 I
13 O
27 O
29 I
5 O
9 O
Level Shifter
28
C1+
25
C1-
1
C2+
3
C2-
RI 24
T1IN
23
DCD
T2IN
RX 22
T3IN
19
CTS
T4IN
17
DSR
T5IN
16
R1OUTB
21
DTR
R2OUT
TX
20
R3OUT
18
RTS
R4OUT
13
Vcc
ON
MAX 3238
*This application note is valid for Vcc> 3.0 Volt (see MAX 3238 specifications)
Auto shut down mode is not used in this example.
Level Shifter Application Diagram for Serial Link
Chapter 3 – Electrical Characteristics
I/O Type* Description
CMOS Transmit serial data
1X Receive serial data
CMOS Ready to send
1X Clear to send
1X Data set ready
CMOS Data terminal ready
CMOS / 2X Data carrier detect
CMOS / 2X Ring indicator
Terminal
27
2
GND
26
4
S_RI
5
T1OUT
6 S_DCD
T2OUT
S_RX
7
T3OUT
S_CTS
10
T4OUT
S_DSR
12
T5OUT
S_DTR
8
R1IN
S_TX
9
R2IN
S_RTS
11
R3IN
15
ERROR
14
Vcc
OFF
Vcc
Vcc
GND
16