Ps2 Interface - HP Visualize J200 Reference Manual

PS2 interface

J Class implements the keyboard and mouse interfaces as simple serial ports conforming to the de facto
industry standard PS/2 specification. Each user input device has a dedicated serial port of its own. LASI
includes two ports, one for keyboard and one for mouse. The interface ports rely on the software to
provide all of their intelligence. Therefore, they do not interpret the characters passing through them in
either direction. The interface to the host processor is through 6 one–byte registers for each port.
Table 4–4 shows the PS/2 interface registers.
Register
Label
ID ID Register
RESET Interface reset register
RCVDATA Received data register
XMTDATA Transmit data register
CONTROL Control register––read/write
STATUS Status register––read only
Note 1: Each PS2 device returns a unique hardwired ID code in bits 3:0 of ID.
Note 2: Resetting the block disables it.
Table 4–5 shows the PS/2 ID register.
Bit Symbol Name
3:0 ID ID Code
7:4 Reserved
Any write to this register will cause the interface to be reset: all buffers will be emptied and the
receive/transmit state machines will be reset. The value of the data written will be discarded. Note that
this does not cause the external device to be reset; it must be reset explicitly through a command sent from
the host. A reset will leave the interface in the disabled state.
Table 4–4. PS/2 Interface Registers
Register Name
Table 4–5. PS/2 ID Register
Description
Hardwired physical identification bits. (0=key-
board;1=mouse)
Address offset Reset
(word Value
aligned)
0x00 note 1
0x00 0xXX
0x04 0xXX
0x04 0xXX
0x08 0x00
note 2
0x0c 0x00
Access
R
W
R
W
R/W
R