CHAPTER 24 SIU (SERIAL INTERFACE UNIT)
473
24.2.9 SIUMC (0x0C00 0004)
Bit
D7
D6
D5
D4
D3
D2
D1
D0
Name
Reserved
Reserved
Reserved
MCR[4]
MCR[3]
MCR[2]
MCR[1]
MCR[0]
R/W
R
R
R
R/W
R/W
R/W
R/W
R/W
RTCRST
0
0
0
0
0
0
0
0
Other resets
0
0
0
0
0
0
0
0
Bit
Name
Function
D[7..5]
Reserved
Write 0 when writing. 0 is returned after read.
D[4]
MCR[4]
For diagnostic testing (local loopback)
1 : Enable use of local loopback
0 : Disable use of local loopback
D[3]
MCR[3]
OUT2 signal (internal) specification
1 : Output the low-level signal
0 : Output the high-level signal
D[2]
MCR[2]
OUT1 signal (internal) specification
1 : Output the low-level signal
0 : Output the high-level signal
D[1]
MCR[1]
RTS# output control
1 : Output the low-level signal
0 : Output the high-level signal
D[0]
MCR[0]
DTR# output control
1 : Output the low-level signal
0 : Output the high-level signal
This register is used for interface control with a modem or data set (or a peripheral device that emulates a modem).
The settings of bit 3 and bit 2 become valid only when bit 4 is set to 1 (enable use of local loopback).
z
Local Loopback
The local loopback can be used to test the transmit/receive data path in the SIU.
The following operation is executed when bit 4 value = 1.
The transmit block’s serial output (TxD) enters the marking state (logical 1) and the serial input (RxD) to the
receive block is cut off. The transmit shift register’s output is looped back to the receive shift register’s input.
The four modem control inputs (DSR#, CTS#, RI (internal), and DCD#) are cut off and the four modem control
outputs (DTR#, RTS#, OUT1 (internal), and OUT2 (internal)) are internally connected to the corresponding
modem control inputs.
The modem control output pins are forcibly set as inactive (high level). During this kind of loopback mode,
transmitted data can be immediately and directly received.
This function can be used to check on the transmit/receive data bus within the SIU.
When in loopback mode, both transmission and receive interrupts can be used. The interrupt sources are
external sources in relation to the transmit and receive blocks.
Although modem control interrupts can be used, the low-order four bits of the modem control register can be
used instead of the four modem control inputs as interrupt sources.
As usual, each interrupt is controlled by an interrupt enable register.