AP1627 データシートの表示（PDF） - Unspecified

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AP1627

Software module of M3L-bus by using HS-SSC for C16x microcontroller family.

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Software module of M3L-bus by using

HS-SSC for C16X uC family

3

Description of Software

3.1 Software Concept

The M3L-bus is generated by the High-Speed Synchronous Serial Channel of the C16X

microcontroller. The clock frequency of the M3L-bus is 1.0 MHz with 20 MHz CPU of the

microcontroller. The baud rate generator for the SCL line can be determined by the

following formula:

BSSC =

fCPU

2 * (<SSCBR> + 1)

SSCBR = (

fCPU

2 * BaudrateSSC

) -1

<SSCBR> represents the content of the reload register.

For example, SSCBR = (20M/(2*1.0M)) -1 = 9. In order to achieve 1.0 MHz of SCL clock

frequency, SSCBR must be assigned as 09H which is based on 20 MHz CPU clock of

16X microcontroller.

The HS-SSC uses 3 I/O lines for communication; SCLK (P3.13 & DP3.13 = 1) serves as

the clock line, MRST (P3.8 = X, DP3.8 = 0) serves as the serial data input line (master

receive/slave transmit), and MTSR (P3.9 & DP3.9 = 1) serves as the serial data

output(master transmit/slave receive). The P3.8 and P3.9 pins are connected together as

the SDA line for half duplex operation.

The operating mode of the SSC is controlled by the control register SSCCON. It has a

common configuration as the 8 bit data with LSB first, in master mode, high for idle clock

line, and high-to-low transition for leading clock edge. When the M3L- bus is in

transmission mode, configured the SSC to shift transmit data on the leading clock edge.

When the M3L-bus is in reception mode, it is configured to latch receive data on leading

clock edge,

This software module will check the clock line before a byte of data is sent or received. It

also checks for WAIT condition before generating a STOP condition. A time delay of

minimum tDWAIT = 750 ns is needed before checking for WAIT condition after a byte of

data is sent /received or before a next byte of data is sent/received. A time delay is

needed to allow enough time for the slave device to pull down the SCL line if the

execution time of C16X microcontroller is shorter than 750 ns.

Semiconductor Group

8 of 14

AP1627 1.97

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