Modem status register – Rainbow Electronics AT75C310 User Manual
Page 77
AT75C310
77
Modem Status Register
Register Name:
US_MS
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
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.
•
DCTS: Delta Clear to Send
This bit is the Delta Clear to Send indicator. Bit 0 indicates that the NCTS input to the chip has changed state since the
last time it was read by the CPU.
•
DDSR: Delta Data Set Ready
This bit is the Delta Data Set Ready indicator. Bit 1 indicates that the NDSR input to the chip has changed state since
the last time it was read by the CPU.
•
TERI: Trailing Edge Ring Indicator
This bit is the Trailing Edge of Ring Indicator detector. Bit 2 indicates that the NRI input to the chip has changed from a
low to a high state.
•
DDCD: Delta Data Carrier Detect
This bit is the Delta Data Carrier Detect indicator. Bit 3 indicates that the NDCD input has changed state.
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.
•
CTS: Clear to Send
This bit is the complement of the Clear to Send (NCTS) input. If bit 4 (loop) of the MCR is set to a 1, this bit is equiva-
lent to RTS in the MCR.
•
DSR: Data Set Ready
This bit is the complement of the Data Set Ready (NDSR) input. If bit 4 (loop) of the MCR is set to a 1, this bit is equiv-
alent to DTR in the MCR.
•
RI: Ring Indicator
This bit is the complement of the Ring Indicator (NRI) input. If bit 4 (loop) of the MCR is set to a 1, this bit is equivalent
to OUT1 in the MCR.
•
DCD: Data Carrier Detect
This bit is the complement of the Data Carrier Detect (NDCD) input. If bit 4 (loop) of the MCR is set to a 1, this bit is
equivalent to OUT2 in the MCR.
•
FCMS: Flow Control Status
This bit indicates the value of the FCM in the Modem Control Register.
31
30
29
28
27
26
25
24
–
–
–
–
–
–
–
–
23
22
21
20
19
18
17
16
–
–
–
–
–
–
–
–
15
14
13
12
11
10
9
8
–
–
–
–
–
–
–
FCMS
7
6
5
4
3
2
1
0
DCD
RI
DSR
CTS
DDCD
TERI
DDSR
DCTS