HP Dc7700 HP Compaq dx7300 and dc7700 Business PC Technical Reference Guide, 1 - Page 97
I/O Port 64h, CMD/DATA bit of the status register bit <3> to CMD.
UPC - 882780715318
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Input/Output Interfaces I/O Port 64h I/O port 64h is used for reading the status register and for writing commands. A read of 64h by the CPU will yield the status byte defined as follows: Bit Function 7..4 General Purpose Flags. 3 CMD/DATA Flag (reflects the state of A2 during a CPU write). 0 = Data 1 = Command 2 General Purpose Flag. 1 Input Buffer Full. Set (to 1) upon a CPU write. Cleared by IN A, DBB instruction. 0 Output Buffer Full (if set). Cleared by a CPU read of the buffer. A CPU write to I/O port 64h places a command value into the input buffer and sets the CMD/DATA bit of the status register (bit ) to CMD. Table 5-15 lists the commands that can be sent tothe 8042 by the CPU. The 8042 uses IRQ1 for gaining the attention of the CPU. Value 20h 60h A4h A5h A6h A7h A8h Table 5-15. CPU Commands to the 8042 Command Description Put current command byte in port 60h. Load new command byte. Test password installed. Tests whether or not a password is installed in the 8042: If FAh is returned, password is installed. If F1h is returned, no password is installed. Load password. This multi-byte operation places a password in the 8042 using the following manner: 1. Write A5h to port 64h. 2. Write each character of the password in 9-bit scan code (translated) format to port 60h. 3. Write 00h to port 60h. Enable security. This command places the 8042 in password lock mode following the A5h command. The correct password must then be entered before further communication with the 8042 is allowed. Disable pointing device. This command sets bit of the 8042 command byte, pulling the clock line of the pointing device interface low. Enable pointing device. This command clears bit of the 8042 command byte, activating the clock line of the pointing device interface. Technical Reference Guide www.hp.com 5-19