at75c220 ATMEL Corporation, at75c220 Datasheet - Page 98

• Manufacturer Part Number: at75c220
• Description: Smart Internet Appliance Processor Siap
• Manufacturer: ATMEL Corporation

Modem Status Register
Register Name:US_MS
Access Type:Read-only
Reset Value:Undefined
This register provides the current state of the control lines from the modem (or peripheral device) to the CPU. In addition to
this current-state information, four bits of the Modem Status Register provide change information. These bits are set to a
logic 1 whenever a control input from the modem changes state. They are reset to logic 0 whenever the CPU reads the
Modem Status Register.
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Note that whenever bit 0, 1, 2, or 3 is set to logic 1, a modem status interrupt is generated. This is reflected in the modem
status register.
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DCTS: Delta Clear to Send
DDSR: Delta Data Set Ready
TERI: Trailing Edge Ring Indicator
DDCD: Delta Data Carrier Detect
CTS: Clear to Send
DSR: Data Set Ready
RI: Ring Indicator
DCD: Data Carrier Detect
FCMS: Flow Control Status
Bit 0 indicates that the NCTS input to the chip has changed state since the last time it was read by the CPU.
Bit 1 indicates that the NDSR input to the chip has changed state since the last time it was read by the CPU.
Bit 2 indicates that the NRI input to the chip has changed from a low to a high state.
Bit 3 indicates that the NDCD input has changed state.
This bit is the complement of the Clear to Send (NCTS) input.
This bit is the complement of the Data Set Ready (NDSR) input.
This bit is the complement of the Ring Indicator (NRI) input.
This bit is the complement of the Data Carrier Detect (NDCD) input.
This bit indicates the value of the FCM in the US_MC.
DCD
31
23
15
–
–
–
7
30
22
14
RI
–
–
–
6
AT75C220
DSR
29
21
13
–
–
–
5
CTS
28
20
12
–
–
–
4
DDCD
27
19
11
–
–
–
3
TERI
26
18
10
–
–
–
2
DDSR
25
17
–
–
9
–
1
FCMS
DCTS
24
16
–
–
8
0