HCS515 datasheet(9/38 Pages) MICROCHIP

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DS40183E-page 9

HCS515

4.2

Command Mode

4.2.1

MICROCONTROLLER COMMAND

MODE ACTIVATION

The microcontroller command consists of four parts.

The first part activates the Command mode, the sec-

ond part is the actual command, the third is the address

accessed, and the fourth part is the data. The micro-

controller starts the command by taking the clock line

high for up to 500 ms. The decoder acknowledges the

start-up sequence by taking the data line high. The

microcontroller takes the clock line low, after which the

decoder will take the data line low, tri-state the data line

and wait for the command to be clocked in. The data

must be set up on the rising edge and will be sampled

on the falling edge of the clock line.

4.2.2

COLLISION DETECTION

The HCS515 uses collision detection to prevent

clashes between the decoder and microcontroller.

Whenever the decoder receives a valid transmission

the following sequence is followed:

• The decoder first checks to see if the clock line is

high. If the clock line is high, the valid transmis-

sion notification is aborted, and the microcon-

troller Command mode request is serviced.

• The decoder takes the data line high and checks

that the clock line doesn’t go high within 50

μs. If

the clock line goes high, the valid transmission

notification is aborted and the Command mode

request is serviced.

• If the clock line goes high after 50

μs but before

500 ms, the decoder will acknowledge by taking

the data line low.

• The microcontroller can then start to clock out the

80-bit data stream of the received transmission.

FIGURE 4-3:

MICROCONTROLLER COMMAND MODE ACTIVATION

MSB

Command Byte

START Command

TCLKL

TCLKH

TDS

LSB

TSTART

TCMD

TDATA

Address Byte

Data Byte

TADDR

TREQ

TRESP

CLK

μC Data

MSB

LSB

MSB

LSB

TACK

HCS515

Data

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