M16CSLASH29 datasheet(245/499 Pages) RENESAS

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14. Serial I/O

page 221

14.2.3 Functions for Setting an SOUTi Initial Value

If the SMi6 bit in SiC register is set to 0 (external clock), the SOUTi pin output level can be fixed high or low

when not transferring data. However, when transmitting data consecutively, the last bit (bit 0) value of the

last transmitted data is retained between the sccessive data transmissions. Figure 14.39 shows the

timing chart for setting an SOUTi initial value and how to set it.

Figure 14.39 SOUTi Initial Value Setting

Signal written to

SiTRR register

SOUTi (internal)

SMi7 bit

SOUTi pin output

SMi3 bit

Setting the SOUTi

initial value to “H”

Port selection switching

(I/O port

SOUTi)

(i = 3, 4)

Initial value = “H” (3)

Port output

(Example) When “H” selected for SOUTi initial value (1)

(2)

NOTES:

1. This diagram applies to the case where the bits in the SiC register are set as follows:

SMi2 = 0 (SOUTi output), SMi5 = 0 (LSB first) and SMi6 = 0 (external clock)

2. SOUTi can only be initialized when input on the CLKi pin is in the high state if the SMi4bit in the SiC

the SMi4 bit is set to 1 (transmit data output at the rising edge of the transfer clock).

3. If the SMi6 bit is set to 1 (internal clock) or if the SMi2 bit is set to 1 (SOUTi output disabled), this

output goes to the high-impedance state.

Setting of the initial value of S OUTi

output and starting of transmission/

reception

Set the SMi3 bit to 0

(SOUTi pin functions as an I/O port)

Write to the SiTRR register

Serial transmit/reception starts

Set the SMi7 bit to 1

(SOUTi initial value = “H”)

Set the SMi3 bit to 1

(SOUTi pin functions as S OUTi output)

“H” level is output

from the SOUTi pin

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