Xylem H-264 - Manual (Page 7)

ASI v2 Operations (PRELIMINARY)
ALERT Serial Interface (ASI)
Overview
The ALERT Serial Interface (ASI) is a multi-purpose device that accepts ALERT ID and data
reports in variety of serial data formats. It buffers, parses, and converts them to 300 baud FSK
audio signals in binary ALERT format. The device controls power, audio and PTT lines of an
attached transmitter to send a standard ALERT binary format transmission.
Outputs
The ASI transmitter interface is 4 wire, consisting of Switched Battery Power, “Push to Talk”
(PTT), Ground and FSK Audio. The FSK Audio signal is an AC coupled, 200mV, low distortion
sine wave signal suitable for commonly used ALERT RF transmitters, such as Maxon. The
audio level is set with a resistive divider allowing a selection during manufacturing for a
maximum of 707mV RMS FSK Audio for transmitters requiring a different audio level input. The
ASI switches up to 3 Amp of nominal 12V battery power to the transmitter with typically less
than 0.05 V drop at 1 A. The PTT transmitter control output is an NPN open collector.
Serial Inputs
The serial data input interface type, baud rate and message format selection is with 5 (out of an
8 bit) DIP switches. Although various formats are supported, only one format is selectable at
one time. The following signaling modes are supported:
• Asynchronous RS232: Data values are received from a standard RS232 serial port at 300,
1200 or 4800 baud using 8 bit data, no parity, one start bit and one stop bit, with no
hardware or software handshaking. The interface is a 2 wire interface, using a data and a
signal ground. The interface levels meet the EIA RS232 specifications, (i.e. MARK is a
maximum of -3 volts, and SPACE is a minimum of +3 V).
• Asynchronous Logic Levels: This mode differs only in the interface levels from the RS-
232, where nominal Logic Level signals are used in place of RS232. Signaling is
conventional (positive logic): 0 V (gnd) is SPACE (bit value 0) and greater than +3 volts is
MARK (bit value 1). The interface is design to accommodate signals from 3 or 5 volt logic
systems, but can be used for nominal 12 volt systems also.
• Synchronous Logic Levels: The electrical interface levels are Logic Levels (as above). A
clock (or strobe) signal is controlled by the sending device. Each positive clock transition
clocks the bit value on the data line at that time into the ASI. No start or stop bits are used.
The maximum clock rate is 500 Hz (2 milliseconds/bit) and the minimum clock rate is 33 Hz
(30 milliseconds/bit). Minimum clock pulse width, positive or negative, is 1 millisecond, but
otherwise there is no specification on clock duty cycle.
The following two serial input data formats are supported:
• Binary message values: A message consists of four bytes. The first two bytes comprise
the ID value as a binary integer between 0 and 8191. The second two represent the data
value as a binary integer between 0 and 2047. This format is used with asynchronous
(RS232 or Logic Level) and synchronous logic level signaling. Synchronous logic level
signaling requires the binary information be sent ID value first, followed by the data value,
sent as two 16 bit words, sent least significant bit first. Asynchronous signaling requires the
binary information be sent as 2 bytes of ID value first, followed by 2 bytes of data value,
each sent least significant 8 bit byte first, followed by the most significant byte.
• ASCII message values: Each message consists of 8 ASCII characters. The first four
represent the ID and the second four represent the data value. Within each 4 character
number the byte ordering is most significant character first and least significant character
last. All ASCII values other than those representing the digits 0 through 9 are ignored. This
format can only be enabled with asynchronous (RS232 or Logic Level) signaling.