cs5535 National Semiconductor Corporation, cs5535 Datasheet - Page 379

• Manufacturer Part Number: cs5535
• Description: Geode Cs5535 Companion Multi-function South Bridge
• Manufacturer: National Semiconductor Corporation

Revision 0.8
UART/IR Controller Register Descriptions
5.12.3.7
I/O Offset
Type
Reset Value
The function of this register depends on the selected operational mode. When a UART mode is selected, this register pro-
vides the current state as well as state-change information of the status lines from the modem or data transmission module.
When any of the IR modes is selected, the register function is controlled by the setting of the IRMSSL bit of the IRCR2 (see
Section 5.12.8.2 on page 390). If IRMSSL is 0, the MSR register works as in UART mode. If IRMSSL is 1, the MSR returns
the value 30h, regardless of the state of the modem input lines.
When loopback is enabled, the MSR works similarly except that its status input signals are internally driven by appropriate
bits in the MCR since the modem input lines are internally disconnected. Refer to bits 1 to 0 in MCR extended mode or bits
3 to 0 in MCR non-extended mode (see Section 5.12.3.5 on page 376) and to the LOOP and ETDLBK bits at the EXCR1
(see Section 5.12.5.2 on page 383).
A Modem Status Event (MS_EV) is generated if the MS_IE bit in IER is enabled and any of bits 0, 1, 2, or 3 in this register
are set to 1.
Bits 0 to 3 are cleared to 0 as a result of any of the following events:
• A hardware reset occurs.
• The operational mode is changed and the IRMSSL bit is 0.
• The MSR register is read.
In the reset state, bits 4 to 7 are indeterminate as they reflect their corresponding signal levels at MSR_UART[x]_MOD.
Bit
7
6
5
4
3
2
1
0
DCD
7
Modem Status Register (MSR)
Name
DCD
RI
DSR
CTS
DDCD
TERI
DDSR
DCTS
06h
RO
x0h
RI
6
Description
Data Carrier Detect. This is the status of the MOD5 bit in MSR_UART[x]_MOD (see Sec-
tion 5.12.1.1 on page 363).
Ring Indicator. This is the status of the MOD7 bit in MSR_UART[x]_MOD (see Section
5.12.1.1 on page 363).
Data Set Ready. This is the status of the MOD6 bit in MSR_UART[x]_MOD (see Section
5.12.1.1 on page 363).
Clear To Send. This is the status of the MOD4 bit in MSR_UART[x]_MOD (see Section
5.12.1.1 on page 363).
Delta Data Carrier Detect. This bit is the Delta Data Carrier Detect (DDCD) indicator.
When high, this bit indicates that the DCD input has changed state. Reading this register
causes this bit to be cleared.
Trailing Edge Ring Indicator. This bit is the Trailing Edge Ring Indicator (TERI) detector.
When high, this bit indicates that the RI input has changed from a high to low state. Read-
ing this register causes this bit to be cleared.
Delta Data Set Ready. This bit is the Delta Data Set Ready (DDSR) indicator. When high,
this bit indicates that the DSR input has changed state since the last time it was read by the
CPU. Reading this register causes this bit to be cleared.
Delta Clear To Send. This bit is the Delta Clear To Send (DCTS) indicator. When high, this
bit indicates that the CTS input has changed state since the last time it was read by the
CPU. Reading this register causes this bit to be cleared.
MSR (Modem Status Register) Bit Descriptions
MSR (Modem Status Register) Register Map
DSR
5
CTS
4
379
(Continued)
DDCD
3
TERI
2
DDSR
1
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DCTS
0