IBM 4840-563 System Reference - Page 43
RW Control Registers Description, I/O Address Offset Description
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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: SurePOS 500 Model XX3 Technical Reference, v 1.3 81 Page 43 of