Gemalto Cinterion ELS81-US, Hardware Interface Description, Page: 26 / 107

Cinterion
®
ELS81-US Hardware Interface Description
2.1 Application Interface
53
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els81-us_hid_v01.004 2017-09-27
Confidential / Preliminary
Page 26 of 107
2.1.4 Serial Interface ASC0
ELS81-US offers an 8-wire unbalanced, asynchronous modem interface ASC0 conforming to
ITU-T V.24 protocol DCE signalling. The electrical characteristics do not comply with ITU-T
V.28. The significant levels are 0V (for low data bit or active state) and 1.8V (for high data bit
or inactive state). For electrical characteristics please refer to
Table 2 . For an illustration of the
interface line’s startup behavior see Figure 7 .
ELS81-US is designed for use as a DCE. Based on the conventions for DCE-DTE connections
it communicates with the customer application (DTE) using the following signals:
•
Port TXD @ application sends data to the module’s TXD0 signal line
• Port RXD @ application receives data from the module’s RXD0 signal line
Figure 6:
Serial interface ASC0
Features:
•
Includes the data lines TXD0 and RXD0, the status lines RTS0 and CTS0 and, in addition,
the modem control lines DTR0, DSR0, DCD0 and RING0.
• The RING0 signal serves to indicate incoming calls and other types of URCs (Unsolicited
Result Code). It can also be used to send pulses to the host application, for example to
wake up the application from power saving state.
• Configured for 8 data bits, no parity and 1 stop bit.
• ASC0 can be operated at fixed bit rates from 1,200bps up to 921,600bps.
• Autobauding supports bit rates from 1,200bps up to 230,400bps.
• Supports RTS0/CTS0 hardware flow control. The hardware hand shake line RTS0 has an
internal pull down resistor causing a low level signal, if the line is not used and open.
Although hardware flow control is recommended, this allows communication by using only
RXD and TXD lines.
• Wake up from SLEEP mode by RTS0 activation (high to low transition; see Section 3.3.2 ).
Note: The ASC0 modem control lines DTR0, DCD0, DSR0 and RING0 are originally available
as GPIO lines. If configured as ASC0 lines, these GPIO lines are assigned as follows:
GPIO1 --> DTR0, GPIO2 --> DCD0, GPIO3 --> DSR0 and GPIO24 --> RING0. Also, DSR0 is
shared with the SPI_CLK line of the SPI interface and may be configured as such. Configura-
tion is done by AT command (see
[1] ). The configuration is non-volatile and becomes active
after a module restart.