MC68181 Datasheet, PDF (61/119 Pages) Freescale Semiconductor, Inc – Advance Information ROAMING FLEX chip SIGNAL PROCESSOR

Freescale Semiconductor, Inc.
APPENDIX B
SPI PACKETS
All data communicated between the FLEX chip 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 FLEX chip 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 consists of a READY pin and four SPI pins (SS, SCK, MOSI, and MISO).The
SS is used as a chip select for the FLEX chip 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
FLEX chip IC is transmitted on the MISO line.
PACKET COMMUNICATION INITIATED BY THE HOST
When the host sends a packet to the FLEX chip IC, it performs the following steps
(see Figure B-1):
1. Select the FLEX chip IC by driving the SS pin low.
2. Wait for the FLEX chip IC to drive the READY pin low.
3. Send the 32-bit packet.
4. De-select the FLEX chip IC by driving the SS pin high.
5. Repeat steps 1 through 4 for each additional packet.
MOTOROLA
MC68181 Technical Data Sheet
B-1
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