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Technical Reference Guide
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
5-7
Table 5–7
. Serial Interface Control Registers
Table 5-7.
Serial Interface Control Registers
COM1
Addr.
COM2
Addr. Register R/W
3F8h 2F8h Receive Data Buffer
Transmit Data Buffer
Baud Rate Divisor Register 0 (when bit 7 of Line Control Reg. Is set)
R
W
W
3F9h 2F9h Baud Rate Divisor Register 1 (when bit 7 of Line Control Reg. Is set)
Interrupt Enable Register:
<7..4> Reserved (always 0’s)
<3> Modem status interrupt enable (active high) (CTS, DSR, RI, CD)
<2> Rx line status interrupt enable (active high) (Overrun, parity, framing error)
<1> Tx holding register empty interrupt enable (active high)
<0> Baud rate divisor interrupt enable (active high)
W
R/W
3FAh 2FAh Interrupt ID Register:
<7,6> FIFO Enable/Disable: 0 = disable, 1 = enable
<5,4> Reserved
<3..1> Interrupt Source:
000 = Modem status 100,101 = Reserved
001 = TX holding reg. Empty 110 = Character time-out
010 = RX data available 111 = Reserved
011 = RX line status
<0> Interrupt pending (if cleared)
FIFO Control Register:
<7,6> RX Trigger Level: 00 = 1 byte, 01 = 4 bytes, 10 = 8 bytes, 11 = 14 bytes
<5..3> Rerserved
<2> TX FIFO reset (active high)
<1> RX FIFO reset (active high)
<0> FIFO Enable/Disable: 0 = Disable TX/RX FIFO’s, 1 = Enable TX/RX FIFO’s
R
W
3FBh 2FBh Line Control Register:
<7> Register acces control:
0 = RX buffer, TX holding, divisor rate registers are accessable.
1 = Divisor rate register is accessable
<6> Break control (forces SOUT singla low if set)
<5> Stick parity (if set, even parity bit is 0, odd parity bit is 1)
<4> Parity type: 0 = odd, 1 = even
<3> Parity enable: 0 = disabled, 1 = enabled
<2> Stop bit: 0 = 1 stop bit, 1 = 2 stop bits
<1,0> Word size: 00 = 5 bits, 01 = 6 bits, 10 = 7 bits, 11 = 8 bits
R/W
3FCh 2FCh Modem Control Register:
<7..5> Reserved
<4> Internal loopback enabled (if set)
<3> Serial I/F interrupts enabled (if set)
<2> Reserved
<1> RTS signal active (if set)
<0> DTR signal active (if set)
R/W
3FDh 2FDh Line Status Register:
<7> Parity error, framing error, or Break condition (if set)
<6> TX holding and TX shift registers are empty (if set)
<5> TX holding register is empty (if set)
<4> Break interrupt has occurred (if set)
<3> Framing error has occurred (if set)
<2> Parity error has occurred (if set)
<1> Overrun error has occurred (if set)
<0> Data register ready to be read (if set)
R
3FEh 2FEh Modem Status:
<7..4> DCD-, RI-, DSR, CTS (respectively) active (if set)
<3..0> DCD-, RI-, DSR, CTS (respectively) changed state since last read (if set)
R