at75c220 ATMEL Corporation, at75c220 Datasheet - Page 80

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

Interrupt Generation
Each status bit in US_CSR has a corresponding bit in
US_IER and US_IDR that controls the generation of inter-
rupts by asserting the USART interrupt line connected to
the AIC. US_IMR indicates the status of the corresponding
bits.
When a bit is set in US_CSR and the same bit is set in
US_IMR, the interrupt line is asserted.
Channel Modes
The USART can be programmed to operate in three differ-
ent test modes using the field CHMODE in US_MR.
Automatic echo mode allows bit-by-bit re-transmission.
When a bit is received on the RXD line, it is sent to the TXD
line. Programming the transmitter has no effect.
Local loopback mode allows the transmitted characters to
be received. TXD and RXD pins are not used and the out-
put of the transmitter is internally connected to the input of
the receiver. The RXD pin level has no effect and the TXD
pin is held high, as in idle state.
Remote loopback mode directly connects the RXD pin to
the TXD pin. The transmitter and the receiver are disabled
and have no effect. This mode allows bit-by-bit re-transmis-
sion.
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AT75C220
Figure 21. Channel Modes
Remote Loopback
Automatic Echo
Local Loopback
Transmitter
Transmitter
Transmitter
Receiver
Receiver
Receiver
V
DD
Disabled
Disabled
Disabled
Disabled
Disabled
V
DD
RXD
TXD
RXD
TXD
TXD
RXD