![](http://datasheet.mmic.net.cn/370000/UPD30181GM-66-8ED_datasheet_16743710/UPD30181GM-66-8ED_379.png)
User’s Manual U14272EJ3V0UM
379
CHAPTER 20 SERIAL INTERFACE UNIT 2 (SIU2)
20.1 General
The SIU2 is a serial interface that conforms to the RS-232-C communication standard and is equipped with two
one-channel interfaces, one for transmission and one for reception. This unit can be also used as an interface in the
IrDA format by means of register setting.
This unit is functionally compatible with the NS16550 except for the additional clock control logic to permit the
16650 core clock source to be stopped.
Figure 20-1. SIU2 Block Diagram
V
R
4181
UART2
IRDIN/RxD2
IRDOUT/TxD2
RTS2#
Activity Timer 2
DTR2#
DCD2#
clk32k
seclk_siu
UART2_clock
SIU2
Caution No clock is supplied to the SIU2 in the initial state. When using the SIU2, set the MSKSIU18M bit
of the CMUCLKMSK register in the MBA Host Bridge to 1 in advance so that the clock is
supplied.
20.2 Clock Control Logic
The power of the 16550 core can be managed by monitoring activity on the modem status pins and writes to the
transmit buffer.
The clock control logic for the 16550 core monitors activity on the four serial interface input signals; RxD2, RTS2#,
DCD2#, and DTR2#. It also monitors writes to the 16550 transmit buffer. Each source has an associated mask bit
which prevents a source from causing reset of the Activity Timer.
Activity on the RxD2, RTS2#, DCD2# and DTR2# inputs is defined as any change of state (high to low or low to
high). When no unmasked activity has been detected on any of the inputs, and no writes have occurred to the
transmit buffer within the programmed time-out period specified in the Activity Timer block, the UART2_clock is
stopped. The UART2_clock will remain stopped until the activity is detected on the monitored sources.