Cinterion
®
ELS81-US Hardware Interface Description
2.1 Application Interface
53
els81-us_hid_v01.004
2017-09-27
Confidential / Preliminary
Page 28 of 107
2.1.5
Serial Interface ASC1
Four ELS81-US GPIO lines can be configured as ASC1 interface signals to provide a 4-wire
unbalanced, asynchronous modem interface ASC1 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
. For an illustration of the interface line’s startup behavior
The ASC1 interface lines are originally available as GPIO lines. If configured as ASC1 lines,
the GPIO lines are assigned as follows: GPIO16 --> RXD1, GPIO17 --> TXD1, GPIO18 -->
RTS1 and GPIO19 --> CTS1. Configuration is done by AT command (see
: AT^SCFG). The
configuration is non-volatile and becomes active after a module restart.
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 module’s TXD1 signal line
•
Port RXD @ application receives data from the module’s RXD1 signal line
Figure 8:
Serial interface ASC1
Features
•
Includes only the data lines TXD1 and RXD1 plus RTS1 and CTS1 for hardware hand-
shake.
•
On ASC1 no RING line is available.
•
Configured for 8 data bits, no parity and 1 or 2 stop bits.
•
ASC1 can be operated at fixed bit rates from 1,200 bps to 921,600 bps.
•
Autobauding supports bit rates from 1,200bps up to 230,400bps.
•
Supports RTS1/CTS1 hardware flow. 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 hard-
ware flow control is recommended, this allows communication by using only RXD and TXD
lines.