áç
ST16C650A
2.90V TO 5.5V UART WITH 32-BYTE FIFO
REV. 5.0.0
IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the CTS# interrupt (default).
• Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
LOW to HIGH.
4.4
Interrupt Status Register (ISR) - Read-Only
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others queue up for next
service. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt Source
Table, Table 9, shows the data values (bit 0-5) for the six prioritized interrupt levels and the interrupt sources
associated with each of these interrupt levels.
4.4.1
Interrupt Generation:
• LSR is by any of the LSR bits 1, 2, 3 and 4.
• RXRDY is by RX trigger level.
• RXRDY Time-out is by a 4-char plus 12 bits delay timer.
• TXRDY is by TX trigger level and TX FIFO empty (or transmitter empty in auto RS485 control).
• MSR is by any of the MSR bits, 0, 1, 2 and 3.
• Receive Xoff/Special character is by detection of an Xoff or Special character.
• CTS# is when its transmitter toggles the input pin (from low to high) during auto CTS flow control.
• RTS# is when its receiver toggles the output pin (from low to high) during auto RTS flow control.
• Wake-up Indicator: when the UART comes out of sleep mode.
4.4.2
Interrupt Clearing:
• LSR interrupt is cleared by a read to the LSR register.
• RXRDY is cleared by reading data until FIFO falls below the trigger level.
• RXRDY Time-out interrupt is cleared by reading RHR.
• TXRDY interrupt is cleared by a read to the ISR register or writing to THR.
• MSR interrupt is cleared by a read to the MSR register.
• Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received.
• Special character interrupt is cleared by a read to ISR or after the next character is received.
• RTS# and CTS# status change interrupts are cleared by a read to the MSR register.
• Wake-up Indicator is cleared by a read to the ISR register.
27
EXAR [ EXAR CORPORATION ]
