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4.1.4. Register Set Channel 4
Register Set 1 is accessible only if Bit7 of the Line Control Register (LCR, address $37) is set to ’0’. After RESET
Register Set 1 is accessible.
IP-I/O-Base+
READ MODE
WRITE MODE
SIZE
$ 31
$ 33
$ 35
$ 37
$ 39
$ 3B
$ 3D
$ 3F
Receive Holding Reg.
Interrupt Enable Reg.
Interrupt Status Reg.
Line Control Reg.
Modem Control Reg.
Line Status Reg.
Modem Status Reg.
not used
Transmit Holding Reg.
Interrupt Enable Reg.
FIFO Control Reg.
Line Control Reg.
Modem Control Reg.
not used
byte
byte
byte
byte
byte
byte
byte
byte
Table 10: Register Set 1 Channel 4
To get access to Register Set 2 of channel 4 bit 7 of the Line Control Register (LCR, address $37) must be set
to ’1’. The Enhance Feature Register, Xon-1,-2 and Xoff-1,-2 registers are accessible only when LCR is set
to ’$BF’.
IP-I/O-Base+ READ/WRITE
SIZE
Comment
$ 31
$ 33
$ 35
$ 37
$ 39
$ 3B
$ 3D
$ 3F
byte
byte
byte
byte
byte
byte
byte
byte
LCR bit-7 set to ’1’
LCR bit-7 set to ’1’
LCR is set to ’$ BF’
always accessible
LCR is set to ’$ BF
LCR is set to ’$ BF’
LCR is set to ’$ BF’
LCR is set to ’$ BF’
LSB of Divisor Latch
MSB of Divisor Latch
Enhanced Feature Reg.
Line Control Register (LCR)
Xon-1 Word
Xon-2 Word
Xoff-1 Word
Xoff-2 Word
Table 11: Register Set 2 Channel 4
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