EV-2 datasheet(21/44 Pages) CIRRUS

21 / 44 page

CobraNet™ EV-2

Rev. 2.1

Hex Switches

Four pins on the 8051 allow the hex switches to be read. The EV-2 circuitry associated with the

hex switches serves as an example implementing this common CobraNet feature (see

Recommended User Interface Practices section in the CobraNet Programmer’s Manual for a

discussion of use of this scheme). Requirements include a physical (hardware) mapping of the

hex switches to a code (software) within the CM. Some of the requirements to achieve this are

listed below:

Two of the four signals will be control signals: a Shift/Load# signal where Shift is high

and Load is Low. The Load allows for parallel, asynchronous loading of the hex switch

data into a shift register and the Shift allows for serial shifting of data out of that regis-

ter. A clock signal to perform the shifting operation where data changes on the rising

end of the clock. The 74HC165 IC is an example of a part that supports this protocol.

The other two signals are the shifted data output and an input that will be shifted seri-

ally into the shift register concatenating it with the hex data. The intent of this latter

signal is to allow for the possibility of concatenating other data, additonal hex switches

or otherwise, for application specific enhancements.

The software will convert the serial hex data stream to a four-byte ASCII value that

represents the switch settings.

As shown in Figure 6, viewing hex switches from the front, the given switch positions would read

as "CA30" in a software query of the hex switch setting. On the EV-2, the microcontoller is

responsible for reading the switches through the hardware serial interface and converting those

readings to an ASCII representation. This representation is then written to the CM through the

host port. Specifically, the EV-2 microcontroller updates the CM's HMI variable, sysName. Using

SNMP,

the

user

may

query

this

variable.

The

SNMP

response

the

form

"PEAK_AUDIO_EVAL-SWwxyz", where the wxyz represents the hex values of the switches in

ASCII format. In the example shown in Figure 6, a query of sysName would return

"PEAK_AUDIO_EVAL_SWCA30".

Figure 6. Example Switch Setting

EV-2 Datasheet(PDF) 21 Page - Cirrus Logic