ScanTool STN1100 FRPM - Manual (Page 4)

STN1100
4 of 23 www.obdsol.com STN1100FRPMA
4.0 Communicating with the STN11xx
The STN11xx uses a three-wire UART connection
that is CMOS/TTL compatible. The UART settings are:
• 38400 baud (default)
• 8 data bits
• No parity bit
• One stop bit
• No handshaking
The baud rate is software-selectable (see STBR).
Note: The UART Tx pin is configured as an open drain
output and requires a 10 kΩ pull-up resistor. Maximum pull-
up voltage is 5 volts.
Once powered and connected, the STN11xx will
display the welcome prompt:
ELM327 v1.3a
>
The STN11xx sends the ‘>’ (“prompt”) character, to
signal that it is ready for more input. User software
should always wait for the prompt before sending the
next command.
There are three types of commands recognized by
the STN11xx: AT commands, ST commands, and
OBD requests.
The STN11xx is designed to fully emulate the
ELM327 AT command set supported by many
existing OBD software applications. AT commands
begin with “AT” and are intended for the IC. They
cause the STN11xx to carry out some action – change
or display settings, perform a reset, and so on. A list of
supported AT commands can be found in section 5.0.
In order to provide additional functionality while
maintaining compatibility with the ELM327 command
set, the STN11xx supports a parallel ST command
set, described in section 6.0.
OBD requests are messages that are transmitted
on the OBD bus. Only ASCII hexadecimal digits (0-9
and A-F) are allowed in OBD requests.
Only ASCII alpha characters, numbers,
backspaces, and the carriage return are accepted on
the UART, spaces are ignored. All commands must
terminate with a carriage return (0x0D).
By default, responses from the STN11xx are
terminated with a carriage return (0x0D). ATL1
command can be used to have the STN11xx append
line feeds (0x0A) to the carriage returns.
Sending a single carriage return character repeats
the last command.