Hanna Instruments HI 23 - Manual (Page 22)

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As soon as one or more keys are pressed, the appropriate
segments out of 88:88 corresponding to the pressed keys,
will light up on the screen. The correspondence is given
below:
For example, if UP and CAL are pressed together the LCD
will look like this:
The colon is a useful indicator for the correct position
squares.
Note A maximum of two keys may be pressed simultaneously to
be properly recognized.
To exit the keyboard test procedure press LCD, CAL and
SETUP simultaneously.
A I2C failure is detected when the I2C transmission is not
acknowledged or a bus fault occurs for more than a certain
number of attempts (this can be due, for example, to dam-
age sustained by one of the ICs connected to I2C bus).
If so, the controller stops any tasks and displays a perpetual
sliding message “Serial bus error” (i.e. this is a fatal error).
If an invalid date is read from RTC, it is initialized back to the
default date and time (01/01/98 - 00:00).
You can use special setup codes, perform selftest procedures
for LCD, keyboard, EEPROM, relays and LEDs, watchdog.
The operation of these functions is outlined in the setup sec-
tion. The selftest procedures are described in detail in the
following subsections.
DISPLAY SELFTEST
The display selftest procedure consists of lighting up all of the
display segments together. The Display test is announced by
a scrolling "Display test" message.
The segments are lit for a few seconds and then switched
off The segments are lit for a few seconds and then switched
off before exiting the selftest procedure.
KEYBOARD SELFTEST
The keyboard selftest procedure begins with the message “But-
ton test, press LCD, CAL and SETUP together to escape”. The
LCD will then show only a colon.