W83977ATF Datasheet, PDF (56/207 Pages) Winbond – WINBOND I/O

W83977ATF
PRELIMINARY
Bit 4: When this bit is set to a logical 1, the UART enters diagnostic mode by an internal loopback, as
follows:
(1) SOUT is forced to logical 1, and SIN is isolated from the communication link instead of the
TSR.
(2) Modem output pins are set to their inactive state.
(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 .
3.2.4 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.
7 6 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.
Publication Release Date: April 1998
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Revision 0.52