W83977F-A Datasheet, PDF (51/182 Pages) Winbond – WINBOND I/O

W83977F-A/ W83977G-A/ W83977AF-A/ W83977AG-A
(3) Modem input pins are isolated from the communication link and connect internally as DTR
(bit 0 of HCR) → DSR, RTS ( bit 1 of HCR) → CTS, Loopback RI input ( bit 2 of HCR) →
RI and IRQ enable ( bit 3 of HCR) → DCD.
Aside from the above connections, the UART operates normally. This method allows the
CPU to test the UART in a convenient way.
Bit 3: The UART interrupt output is enabled by setting this bit to a logic 1. In the diagnostic mode this
bit is internally connected to the modem control input DCD .
Bit 2: This bit is used only in the diagnostic mode. In the diagnostic mode this bit is internally
connected to the modem control input RI .
Bit 1: This bit controls the RTS output. The value of this bit is inverted and output to RTS .
Bit 0: This bit controls the DTR output. The value of this bit is inverted and output to DTR .
6.2.4 Handshake Status Register (HSR) (Read/Write)
This register reflects the current state of four input pins for handshake peripherals such as a modem
and records changes on these pins.
76 54 321 0
CTS ^{toggling (TCTS)}
DSR ^{toggling (TDSR)}
RI falling edge (FERI)
DCD ^{toggling (TDCD)}
Clear to send (CTS)
Data set ready (DSR)
Ring indicator (RI)
Data carrier detect (DCD)
Bit 7: This bit is the opposite of the DCD input. This bit is equivalent to bit 3 of HCR in loopback
mode.
Bit 6: This bit is the opposite of the RI input. This bit is equivalent to bit 2 of HCR in loopback mode.
Bit 5: This bit is the opposite of the DSR input. This bit is equivalent to bit 0 of HCR in loopback
mode.
Bit 4: This bit is the opposite of the CTS input. This bit is equivalent to bit 1 of HCR in loopback
mode.
Bit 3: TDCD. This bit indicates that the DCD pin has changed state after HSR was read by the
CPU.
Bit 2: FERI. This bit indicates that the RI pin has changed from low to high state after HSR was read
by the CPU.
Bit 1: TDSR. This bit indicates that the DSR pin has changed state after HSR was read by the CPU.
Bit 0: TCTS. This bit indicates that the CTS pin has changed state after HSR was read.
Publication Release Date: May 2006
-43 -
Revision 0.60