Chapter 3 | Hardware |
Real Time Clock (RTC)/Battery
The XTX 820 supports a Real Time Clock (RTC) and CMOS RAM for the BIOS Setup Utility. The RTC and 256 byte of CMOS RAM are included inside the I/O Hub (Southbridge) chip (82801FBM). The RTC and CMOS are powered through
Table
J4 | Signal | Description |
Pin # |
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3 | 5V_SB | 5 volt Suspend – This control signal is sent to the ATX power supply for a |
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| suspend or standby state. |
4 | PWGIN | Power Good In – This active high input signal indicates to the XTX 820, the |
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| power is good and it can begin the boot process. |
5 | PS_ON | Power Supply On – This |
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| to the ATX power supply to turn it on. |
7 | PWRBTN* | Power Button – This signal provides a ground temporarily through an open |
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| collector driver to the ATX power supply to change states (turn it on). |
6 | SPEAKER | Speaker – This PC speaker output signal must be connected to a speaker |
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| (piezoelectric or dynamic) on the baseboard to hear the output (beeps). |
11 | RSMRST* | Resume Reset – This signal is driven low by external circuitry to reset the |
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| power management logic on the XTX 820. |
19 | OVCR | Over Current Detect – This signal indicates a USB |
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|
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8 | BAT | Battery Voltage – This is the + battery connection to baseboard for +3 volt |
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| lithium backup battery used for RTC operation and CMOS |
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| memory. |
41 | BATLOW* | Battery Low – This external signal to the XTX 820 indicates when the |
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| external battery is low. |
21 | EXTSMI* | Extern System Management Interrupt – This signal is provided by external |
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| circuitry to initiate an SMI event with the XTX 820. |
23 | SMBCLK | System Management Bus Clock – This signal is used to support internal and |
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| external SMBus devices, such as temperature and battery monitoring. |
24 | SMBDATA | System Management Bus Data – This signal is used to support internal and |
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| external SMBus devices, such as temperature and battery monitoring. |
26 | SMBALRT* | System Management Bus Alert – This signal is used by SMBus devices to |
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| signal an event on the SM Bus. |
Note: The shaded area denotes power or ground.
SMBus (I2C Bus)
The I/O Hub (82801FBM) contains an integrated SMBus controller with both a host and slave SMBus port; but the host cannot access the slave internally. The slave port allows an external master access to the I/O Hub (Southbridge) through the J4 connector. The master contained in the I/O Hub is used to communicate with the Memory & Graphics Hub, DDR2 RAM EPROM, and the clock generator.
•The I2C slave address must not be the same as the I2C device on the baseboard.
50 | Reference Manual | XTX 820 |