HCS500-IP datasheet(8/24 Pages) MICROCHIP

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HCS500

DS40153B-page 8

Preliminary

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 second

part is the actual command, the third is the address

accessed, and the last part is the data. The microcon-

troller 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 micro-

controller 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 clock 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 HCS500 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 microcontrol-

ler 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

HCS500

Data

MSB

LSB

MSB

LSB

TACK

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