IBM 4840-563 System Reference Manual page 43

Interrupt Status Register A (Read Only)
Offset 41h
Bit
3 Status of UART 3 Interrupt Status (0: No Interrupt, 1: Interrupt Asserted)
2 Status of UART 2 Interrupt Status (0: No Interrupt, 1: Interrupt Asserted)
1 Status of UART 1 Interrupt Status (0: No Interrupt, 1: Interrupt Asserted)
0 Status of UART 0 Interrupt Status (0: No Interrupt, 1: Interrupt Asserted)
The UARTs are compatible with standard 16550 FIFO UARTs. Refer to datasheet of 16550
for the details on how interrupts are cleared via the UART's registers.
RW Control Registers Description
All the I/O related registers are handled through the PCI Base Address Register (BAR) at offset of 10h of the
PCI Config Space. During the PCI initialization, 16 bytes of I/O space will be allocated for the following control
registers for the control of various I/O devices:
I/O Address Offset Description
00h Presence Sensor Control Register
01h Function 0 Interrupt Status Register
02h EEPROM Control Register
03h UART Control Register
04h Distributed VFD Register
05h VFD Register 1
06h - Keyboard Control Register
07h - 0Fh - Reserved
Presence Sensor Control Register 0 (Read/Write) Register offset 00h
Bit 0: Presence detect (0: Detected, 1: Not Detected, i.e. active low.) Reflects the detect signal coming from
the Presence Sensor circuit (pin E_DETECT#) Read only. This bit is only valid when interrupt mode is
inabled.
Bit 1: Calibrate (0: Calibration not active, 1: Calibration is activated, power-up value is 1.) To enable the
trigger of calibration, software needs to write a "1" to this bit. The power up default = 0. When trigger is
enabled (i.e. Bit 1 = 1), the Calibrate signal (pin E_CALIBRATE) will go active (high) when the input signal
(pin E_CALIBRATE_TRG) is high (being triggered from the 8051).
Bit 2: Presence sensing enable/disable (0: Disable, 1: Enable, power-up value us 1) read/write bit with
power-up value as 0. It is used to enable/disable the presence sensor function.
The polled Presence Sensor status can be read via the following steps:
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