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STX
Address (hex)
Data
ETX
1 byte
1 byte
n bytes
1 byte
Do not add CR character.
Total bytes = n + 3
XON
Address (hex)
Data
XOFF
1 byte
1 byte
n bytes
1 byte
For STROBE MODE add CR (0D hex) to the data.
Total bytes = n + 3
7.3.- INSTRUMENT ADDRESSING.
Having received the ETX or XOFF character, start the addressing sending the STX or XON character, the next
character received is the address of the unit that is to receive data.
There are 32 possible addresses, from code 30 to code 4F hex. These correspond to addresses set up on the switch
jumper on the card. Selector S4.
After address character send data characters followed by a character XOFF or ETX to stop the data reception and
finish the address selection.
Units with the address, "0" (ASCII 30 hex), will display all data, including the address code sent, and this address will
cause any unit to receive data.
The instrument powers-up in the listening condition, so ETX or XOFF must be sent to the unit to start the addressing
mode.
Note the ETX character is treated as a carriage return character, in addition to an XOFF character, strobing the last
string into the display.
When using ETX, STX as separators for data strings the CR character should be omitted from the end of strings, else
a blank display will result.
MESSAGE FORMAT IN ASCII PROTOCOL
7.4.- OVERLOAD AND POLARITY INDICATORS
The overload indicator is the upper bar of the 7th character.
The polarity indicator is the middle bar of the 7th character.
This applies even to a 4 digit display, so to light up the overload or polarity indicator, characters 5 and 6 must be padded
out with any printable character.
To light the polarity indicator, any character that indicates the middle bar but excludes the upper bar should be sent
to the display (for example -) to light the overload indicator, a character that includes the upper bar but excludes the
middle bar should be sent (for example 0, or : ). To light both overload and polarity indicators the character sent must
include both bars (for example ?).
7.5.- BS4505 SUBSET
The display powers-up responding to and, if appropriate, displaying the characters sent to it. Having received the
character EOT, the display switches to respond to a sub-set of the BS4505 protocol. The four characters received by
the display subsequent to EOT are the group number sent twice and the ID number sent twice. If the characters are
equivalent to the address of the display (set by internal jumper switches) the display switches to a listening condition,
else it ignores any further characters until EOT is again transmitted. Once listening, the STX character is used to start
recognition and display characters, and ETX is used as a terminator to strobe data into the display and stop further
recognition and display characters. Note that data strings terminated by carriage return should not be used, since
carriage return followed by ETX will result in a blank display. The display is a dumb receiver. and provides no response
to messages. The block check characters are not used, and the leading alpha characters following STX are treated
as printable characters and will appear on the display, if the character string is short enough.
EQUIVALENT ADDRESSES
The combination of Group (G) and ID numbers allows for addresses 1 to 31. The relationship between these
addresses, and the switch settings of the display is as shown on page 14.
It is not necessary to send again the sequence [EOT] [G] [G] [ID] [ID] to keep the address selected.
MESSAGE FORMAT IN ASCII PROTOCOL
EOT
G
G
ID
ID
STX
Data
ETX
STX
1 byte
4 bytes
1 byte
n bytes
1 byte
DATA
: In units with 6 digit display only the 6 last characters will be displayed, and the 4 last characters if the
unit is a 4 digit display.