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APPENDIX B

SPI PACKETS

All data communicated between the FLEXchip IC and the host MCU is transmitted on the SPI in 32-bit packets. Each packet consists of an 8-bit ID followed by 24 bits of information. The FLEXchip IC uses the SPI bus in Full Duplex mode. In other words, whenever a packet communication occurs, the data in both directions is valid packet data.

The SPI interface consists of a READY pin and four SPI pins (SS, SCK, MOSI, and MISO).The SS is used as a chip select for the FLEXchip IC. The SCK is a clock supplied by the host MCU. The data from the host is transmitted on the MOSI line. The data from the FLEXchip IC is transmitted on the MISO line.

PACKET COMMUNICATION INITIATED BY THE HOST

When the host sends a packet to the FLEXchip IC, it performs the following steps (see Figure B-1):

1.Select the FLEXchip IC by driving the SS pin low.

2.Wait for the FLEXchip IC to drive the READY pin low.

3.Send the 32-bit packet.

4.De-select the FLEXchip IC by driving the SS pin high.

5.Repeat steps 1 through 4 for each additional packet.

SS

1

 

4

 

 

 

 

 

 

READY

2

 

 

 

 

 

 

 

 

SCK

3

 

 

 

 

 

 

 

 

MOSI

D31

D1

D0

D31

D1

D0

D31

D1

D0

MISO

D31

D1

D0

D31

D1

D0

D31

D1

D0

 

 

 

 

High impedance state

 

 

 

Figure B-1 Typical Multiple Packet Communications Initiated by the Host

MOTOROLA

MC68175/D, Preliminary

B-1

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