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SPI Packets

Packet Communication Initiated by the FLEXchip IC

When the host sends a packet, it will also receive a valid packet from the FLEXchip IC. If the FLEXchip IC is enabled (See Checksum Packet on page B-6.) and has no other packets waiting to be sent, the FLEXchip IC will send a status packet. The host must transition the SS pin from high to low to begin each 32-bit packet. The FLEXchip IC must see a negative transition on the SS pin in order for the host to initiate each packet communication.

PACKET COMMUNICATION INITIATED BY THE FLEXCHIP IC

When the FLEXchip IC has a packet for the host to read, the following occurs (see

Figure B-2):

1.The FLEXchip IC drives the READY pin low.

2.If the FLEXchip IC is not already selected, the host selects the FLEXchip IC by driving the SS pin low.

3.The host receives (and sends) a 32-bit packet.

4.The host de-selects the FLEXchip IC by driving the SS pin high (optional).

SS

2

 

4

 

 

 

 

 

 

READY

1

 

 

 

 

 

 

 

 

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-2 Typical Multiple Packet Communications Initiated by the FLEXchip IC

When the host is reading a packet from the FLEXchip IC, it must send a valid packet to the FLEXchip IC. If the host has no data to send, it is suggested that the host send a Checksum Packet with all of the data bits set to 0 in order to avoid disabling the FLEXchip IC. (See Checksum Packet on page B-6.)

B-2

MC68175/D, Preliminary

MOTOROLA

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