The Human Interface Board; Data Transfer; Sound Generation; Volume Control - HP M2350A Service Manual

Understanding the Display Module
The Human Interface Board
The Human Interface Board
The Human Interface board controls the interface between the user and the system. This board
comprises the following functions:
l
HP HIL control (HP Human Interface Link),
n
Sound generation and audio power amplification,
n
Lamp (LED) control and driver,
w Key pad scanning,
w Key encoding,
n
Key code transmission to the Computer Module via the HP HIL,
w Brightness and Contrast controls.
Data Transfer
Data transfer to and from the Computer Module is performed serially via the HP HIL using
the transmit/receive circuit called CHARON. This device sends data in response to a POLL
command and receives data from the HIL master using the WRITE REGISTER command. The
received data is used to:
w Control the various lamp indicators (LEDs) located on the keypad
n
Activates or triggers the audible tones prompts),
n
Enables or disables on-board functions
Sound Generation
The Human Interface board generates an audible tone for various conditions; each condition
has its own tone to prevent ambiguity. Each tone has its own control word which, when sent
to the processor, generates the required tone.
The tones for non-alarm conditions are derived directly from the processor. The alarm tones
are processor-generated, based on variable frequency steps.
Volume Control
The Human Interface board has two volume controls:
n
Alarms
n
Miscellaneous
Both controls function in the same manner. The analog tone is applied to the Vref input of a
DAC, the digital input to the DAC is the volume control. The attenuated tone (DAC output) are
summed and input to the power amplifier for the loud speaker.
3.6