Specifications

Select the

command

Disable the

Atmel SPI

module

Write each bit

to the data

line and toggle

the clock

Enable the

Atmel SPI

module

Select the

data register

Figure 15 Writing data to the decoder command register

To write to the configuration register, the hardware SPI module of the Atmel

ATmega103 cannot be used because the configuration of the data is not a standard 8-bit

packet. The data consists of 4-bits for an op-code (used to tell the decoder if the user is

writing or reading data), 4-bits for the command register required (there is more than

one command register) and then 16-bits for the data. The sending of this packet is done

by masking out each bit and placing it on the data line (SI pin) of the decoder then

raising the clock for a few clock cycles and lowering it again. This process is repeated

for all the 24bits and then the SPI module is enabled again and the data register is

selected ready to receive data.

Lower the

byte sync line

Place data into

the SPI register

Wait 6 clock

cycles

Raise the byte

sync line

Wait for SPI

to finish

Figure 16 Writing data to the decoder data register

Figure 16 displays the operations required to send data to the decoder’s data register.

The data register is selected already selected so is not required; the write begins by

raising the byte sync line which is used to tell the decoder that data is being sent. The

data is then placed into the Atmel’s SPI shift register which handles the sending of the

data. After a few clock cycles the byte sync line is then lowered and the function waits

until the SPI transfer is finished and the exits.