
16.1.4.1 SSi Input Pin Function (i = 0 to 4)
When the SSE bit in the UiSMR3 register is set to 1 (SS function enabled), the SSi input pin function is
enabled.
The DINC bit in the UiSMR3 register determines whether the MCU performs as a master or slave.
When multiple MCUs perform as masters (multi-master system), the SSi pin state determines which master
MCU is active each time.
16.1.4.2 When Setting the DINC Bit to 1 (Slave Mode)
When a high-level (“H”) signal is applied to the SSi pin, the STXDi pin is placed in a high-impedance state and
the serial clock input to the CLKi pin is ignored. When a low-level (“L”) signal is applied to the SSi input pin,
the serial clock input and serial communication are enabled.
16.1.4.3 When Setting the DINC Bit to 0 (Master Mode)
To use the SSi pin function in master mode, set the UiIRS bit in the UiC1 register to 1 (transmit operation
completion is selected as UARTi transmit interrupt source). When an “H” signal is applied to the SSi pin, the
MCU is given the privilege of transmitting and serial communication becomes available. The master outputs
the serial clock. When an “L” signal is applied to the SSi pin, it indicates another master is active and pins
TXDi and CLKi are placed in high-impedance states. Moreover, the EER bit in the UiSMR3 register is set to 1
(mode error occurred). Verify whether a mode error has occurred or not with the EER bit in the transmit
complete interrupt routine.
To resume serial communication after a mode error occurs, set the ERR bit to 0 (no mode error occurred) while
an “H” signal is applied to the SSi pin. Pins TXDi and CLKi are placed in output states.
Figure 16.24
Serial Bus Communication Control with SSi Pin
MCU
P1_3
P1_2
P9_3(SS3)
P9_0(CLK3)
P9_1(RXD3)
P9_2(TXD3)
MCU
(Slave)
(Master)
P9_3(SS3)
P9_0(CLK3)
P9_1(STXD3)
P9_2(SRXD3)
P9_3(SS3)
P9_0(CLK3)
P9_1(STXD3)
P9_2(SRXD3)
(Slave)