ATAM894 datasheet(64/97 Pages) ATMEL

64 / 97 page

4679D–4BMCU–05/05

ATAM894

6.3.4.5

9-bit Shift Mode

In the 9-bit shift mode, the SSI is able to handle the MCL protocol (described below). It always

operates as an MCL master device, i.e., SC is always generated and output by the SSI. Both the

MCL start and stop conditions are automatically generated whenever the SSI is activated or

deactivated by the SIR bit. In accordance with the MCL protocol, the output data is always

changed in the clock low phase and shifted in on the high phase.

Before activating the SSI (SIR = 0) and commencing an MCL dialog, the appropriate data direc-

tion for the first word must be set using the SDD control bit. The state of this bit controls the

direction of the data port (BP43 or MCL_SD). Once started, the 8 data bits are, depending on

the selected direction, either clocked into or out of the shift register. During the 9th clock period,

the port direction is automatically switched over so that the corresponding acknowledge bit can

be shifted out or read in. In transmit mode, the acknowledge bit received from the slave device is

captured in the SSI Status Register (TACK) where it can be read by the controller. In receive

mode, the state of the acknowledge bit to be returned to the slave device is predetermined by

the SSI Status Register (RACK).

Changing the directional mode (TX/RX) should not be performed during the transfer of an MCL

telegram. One should wait until the end of the telegram which can be detected using the SSI

interrupt (IFN = 1) or by interrogating the ACT status.

Once started, a 9-bit telegram will always run to completion and will not be prematurely termi-

nated by the SIR bit. So, if the SIR bit is set to '1' in telegram, the SSI will complete the current

transfer and terminate the dialog with an MCL stop condition.

Figure 6-42.

Example of MCL Transmit Dialog

7 6 543 21

76 54 32 10 A

msb

lsb

tx data 1

tx data 2

msb

lsb

Write STB

(tx data 1)

SRDY

ACT

Interrupt

(IFN = 0)

Interrupt

(IFN = 1)

Write STB

(tx data 2)

SIR

SDD

Start

Stop

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