HCS500T-ISLASHST datasheet(10/42 Pages) MICROCHIP

10 / 42 page

HCS500

DS40000153E-page 10

 2001-2015 Microchip Technology Inc.

FIGURE 4-2:

DECODER VALID TRANSMISSION MESSAGE

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

microcontroller 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 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

transmission notification is aborted, and the

microcontroller Command mode request is

serviced.

• The decoder takes the data line high and checks

that the clock line does not go high within 50

s. 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

s 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

Decoder Signal Valid

TCLKH

TDS

Cii

TPP3

TDHI

TCLA

Received String

S_DAT

TX0

TX3

X63

REPT VLOW S0

CNT0

CNT3

X62

S_CLK

Information

TPP1

TCLKH

TCLKL

Transmission

MSB

Command Byte

Start Command

TCLKL

TCLKH

TDS

LSB

TSTART

TCMD

TDATA

Address Byte

Data Byte

TADDR

TREQ

TRESP

CLK

C Data

Decoder

Data

MSB

LSB

MSB

LSB

TACK

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