68HC05CL48 datasheet(73/145 Pages) MOTOROLA

73 / 145 page

June 11, 1997

GENERAL RELEASE SPECIFICATION

MC68HC05CL48

SERIAL PERIPHERAL INTERFACE

MOTOROLA

REV 2.0

9-1

SECTION 9

SERIAL PERIPHERAL INTERFACE

The term “serial peripheral” refers to the fact that this interface requires separate

wires (signals) for data and clock. In this format, data does not contain an explicit

clock. The SPI scheme may be used to interconnect microcomputers located at a

short distance (usually within a single “black box” or on the same PC card). This

may comprise a system of one microcomputer and several slaves or may be a

system of microcomputers, each having the capability of either master or slave.

A practical system may include:

1) MISO master in slave out

2) MOSI master out slave in

3) SCK serial clock

4) SS (n) slave select(s)

9.1

SIGNAL DESCRIPTION

9.1.1 MISO Master In Slave Out

9.1.1.1

Slave Mode

MISO is the signal which is used in Slave Mode to present data from a Slave

device to the bus. The MISO pin will be placed in the hi-Z state whenever a Slave

device is “not” selected (SS=1) by the bus master. Figure 9-1 shows the clock

(SCK) and data relationship. Four possible timing relationships may be chosen by

use of the control bits (CPOL) and (CPHA). The Slave device and a Master device

must be programmed to be in similar timing modes for proper data transfer.

9.1.1.2

Master Mode

In the master mode (control bit MSTR=1), the function of MOSI and MISO are

inverted within the device. Therefore, the MISO pin becomes the data input pin for

a device which is in the master mode. (Also, the function of SCK switches from

being an input for system clock to one of outputting the system clock.)

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