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

1 Introduction to M3L-bus

The M3L-bus is a single master protocol which consists of 3-wire bus; the SCL(clock),

SDA(data), and I2CEN (for START and STOP condition). The clock frequency can

achieve up to 1.0 MHz that means faster data transfer rate as the I2C Bus. The

microcontrollers from Siemens have a hardware interface which can be used for M3L-bus

protocol. This software module is using the hardware peripheral of High-Speed

Synchronous Serial Channel for the C16X microcontroller family.

2 M3L-bus Specification

2.1 Data Transfer formats

When there is a HIGH to LOW transition on the I2CEN line, it indicates a START

condition. A LOW to HIGH transition on the I2CEN is defined as the STOP condition. The

data line can only be changed when the clock signal on the SCL line is HIGH. Therefore,

the data on the SDA line must be stable during the LOW period of the clock signal.

Each information puts on the SDA line must be 8-bit long. There is no acknowledge bit

followed by every byte sent for this M3L-bus protocol. The reason for not implement the

acknowledge bit is that the MegaText IC comes with input filter in the SDA and SCL lines

which will suppress high-frequency interference on those lines.

In M3L-bus mode, the LSB of the data is transmitted first. For example, if the chip

selected address is MSB R/W 1000100 LSB, then the data on the SDA line will be LSB

0010001(R/W) MSB. The difference from I2C is that the READ/WRITE bit is on the MSB

position. The write select address will be 44H, and read select address in this case is

C4H. If the transmitted or received data is MSB 10110001 LSB, the data on the SDA line

will be LSB 10001101 MSB. The USART peripheral of the Siemens’ microcontroller will

be sending and receiving the LSB bit first. The data of transmit and receive shift registers

are in the normal format MSB xxxxxxxx LSB. Therefore, there is no additional software

involved for any conversion of data.

There are only two basic types of data transfer format for M3L-bus. Figure #1 shows the

M3L -bus data transfer format of writing data from microcontroller/master to

MegaText/slave. Figure #2 shows the data transfer format of reading data from the

MegaText/slave to microcontroller/master.

Semiconductor Group

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AP1627 1.97

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