VT82C686B
Interrupt Controller Registers
Interrupt Controller Shadow Registers
The following shadow registers are enabled by setting function
0 Rx47[4]. If the shadow registers are enabled, they are read
back at the indicated I/O port instead of the standard interrupt
controller registers (writes are unchanged).
Ports 20-21 - Master Interrupt Controller
The Master Interrupt Controller controls system interrupt
channels 0-7. Two registers control the Master Interrupt
Controller. They are:
I/O Address Bits 15-0 Register Name
Port 20 - Master Interrupt Control Shadow ................... RO
Port A0 - Slave Interrupt Control Shadow ..................... RO
0000 0000 001x xxx0
0000 0000 001x xxx1
Master Interrupt Control
Master Interrupt Mask
RW
RW
........................................always reads 0
7
6
5
4
3
2
1
0
Reserved
OCW3 bit 2 (POLL)
OCW3 bit 0 (RIS)
OCW3 bit 5 (SMM)
OCW2 bit 7 (R)
Note that not all bits of the address are decoded.
The Master Interrupt Controller is compatible with the Intel
8259 Interrupt Controller chip. Detailed descriptions of 8259
Interrupt Controller operation can be obtained from the Intel
Peripheral Components Data Book and numerous other
industry publications.
ICW4 bit 4 (SFNM)
ICW4 bit 1 (AEOI)
ICW1 bit 3 (LTIM)
Port 21 - Master Interrupt Mask Shadow....................... RO
Port A1 - Slave Interrupt Mask Shadow ........................ RO
Ports A0-A1 - Slave Interrupt Controller
........................................always reads 0
7-5 Reserved
The Slave Interrupt Controller controls system interrupt
channels 8-15. The slave system interrupt controller also
occupies two register locations:
4-0 T7-T3 of Interrupt Vector Address
Timer / Counter Registers
I/O Address Bits 15-0 Register Name
Ports 40-43 - Timer / Counter Registers
There are 4 Timer / Counter registers:
0000 0000 101x xxx0
0000 0000 101x xxx1
Slave Interrupt Control
Slave Interrupt Mask
RW
RW
I/O Address Bits 15-0 Register Name
Note that not all address bits are decoded.
0000 0000 010x xx00
0000 0000 010x xx01
0000 0000 010x xx10
0000 0000 010x xx11
Timer / Counter 0 Count
Timer / Counter 1 Count
Timer / Counter 2 Count
Timer / Counter Cmd Mode
RW
RW
RW
WO
The Slave Interrupt Controller is compatible with the Intel
8259 Interrupt Controller chip. Detailed descriptions of 8259
Interrupt Controller operation can be obtained from the Intel
Peripheral Components Data Book and numerous other
industry publications.
Note that not all bits of the address are decoded.
The Timer / Counters are compatible with the Intel 8254
Timer / Counter chip. Detailed descriptions of 8254 Timer /
Counter operation can be obtained from the Intel Peripheral
Components Data Book and numerous other industry
publications.
Timer / Counter Shadow Registers
The following shadow registers are enabled for readback by
setting function 0 Rx47[4]. If the shadow registers are
enabled, they are read back at the indicated I/O port instead of
the standard timer / counter registers (writes are unchanged).
Port 40 – Counter 0 Base Count Value (LSB 1st MSB 2nd)RO
Port 41 – Counter 1 Base Count Value (LSB 1st MSB 2nd)RO
Port 42 – Counter 2 Base Count Value (LSB 1st MSB 2nd)RO
Revision 1.71 June 9, 2000
-43-
Register Descriptions - Legacy I/O Ports
ETC [ ETC ]
