Rev. 3.0, 03/01, page 166 of 390
(2) UMSR (READ/WRITE)
This 8-bit register provides current state of the control lines from modems or peripheral devices. In
addition to this current state information; bits 7~ 4 can provide change information when a modem
control input changes state. It will be reset to low when the Host reads the UMSR.
Bit
Description
Default
7
Data Carrier Detect (DCD#): Indicates the complement status of Data Carrier Detect
input. If bit 4 of UMCR is 1, this bit is equivalent to OUT2 of the UMCR.
-
6
Ring Indicator (RI#): Indicates the complement to the RI# input. If bit 4 of UMCR is 1, this
bit is equivalent to OUT1 in the UMCR.
-
5
Data Set Ready (DSR#): Indicates the modem is ready to provide received data to the
serial channel receiver circuitry. If the serial channel is in the loop mode (bit 5 of UMCR is
1), this bit is equivalent to DTR# in the UMCR.
-
4
Clear to Send (CTS#): Indicates the complement of CTS# input. If the serial channel is in
the loop mode (bit 4 of UMCR is 1), this bit is equivalent to RTS# in the UMCR.
-
3
Delta Data Carrier Detect (DDCD): Indicates that the DCD# input state has been
changed since the last time read by the Host.
-
2
Trailing Edge of Ring Indicator (TERI): Indicates that the RI input state to the serial
channel has been changed from a low to high since the last time read by the Host. The
change to logic 1 doesn’t activate the TERI.
-
1
Delta Data Set Ready (DDSR): A logic “1” indicates that the DSR# input to the serial
channel has changed state since the last time it was read by the Host.
-
0
Delta Clear to Send (DCTS): This bit indicates that the CTS# input state to the serial
channel has been changed since the last time it was read by the Host
-
Table 12.6
Modem Status Register Bits
Bit
Mnemonic
Logic 0
7
DCD#
Data Carrier Detect
6
RI#
Ring Indicator
5
DSR#
Data Set Ready
4
CTS#
Clear To Send
3
DDCD
Delta Data Carrier Detect
2
TERI
Trailing Edge of Ring Indicator
1
DDSR
Delta Data Set Ready
0
DCTS
Delta Clear to Send
Summary of Contents for HD64465
Page 25: ...Rev 3 0 03 01 page 6 of 390 ...
Page 59: ...Rev 3 0 03 01 page 40 of 390 ...
Page 97: ...Rev 3 0 03 01 page 78 of 390 ...
Page 147: ...Rev 3 0 03 01 page 128 of 390 ...
Page 199: ...Rev 3 0 03 01 page 180 of 390 ...
Page 247: ...Rev 3 0 03 01 page 228 of 390 ...
Page 385: ...Rev 3 0 03 01 page 366 of 390 ...
Page 389: ...Rev 3 0 03 01 page 370 of 390 ...
Page 409: ...Rev 3 0 03 01 page 390 of 390 ...