Motorola MC68328 Technical Information PDF herunterladen (Seite 22)

3-4

FLEX Alphanumeric Chip MC68175 Interface

Software Development

FLEX System Software

3.1.2 SPI Communication

The FLEX Alphanumeric Chip IC communicates with the host MCU via SPI in 32-bit

packets. Each packet consists of an 8-bit ID followed by twenty-four bits of data. The

FLEX IC uses SPI in Full Duplex mode; that is, for every transfer, both the FLEX IC and

host MCU transmit and receive valid information.

The SPI consists of a READY

pin and four SPI pins: SS, SCK, MOSI, and MISO, as

described in the hardware section. When the host sends a packet to the FLEX

Alphanumeric Chip IC, it first selects the FLEX IC by driving the SS

pin low. When the

FLEX IC has a packet for the host to read, it drives the READY

line low to assert an

interrupt to the host.

3.1.3 Enabling the FLEX Alphanumeric Chip

Depending on the upper 8-bit ID value, data packets can be classified and recognized by

the FLEX Alphanumeric Chip and FLEX One-Way Stack software running on the host

microprocessor. For example, a packet with an ID of “00” is a

Checksum

packet, while a

packet with an ID of “01” is the

Configuration

packet, etc. One of the packets that the

FLEX Alphanumeric Chip sends to the host MPU is the

Part ID

packet (ID = “FF”),

which was designed to ensure proper communication procedure between the host and

the FLEX IC.

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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Motorola MC68328 Technical Information Seite 22