CPU External Clock Jumpers
If you are installing an i486DX, or i486SX the internal CPU clock speed is
the same as the external CPU clock speed. This is different for i486DX2
CPU where the external speed is one-half of the internal speed. For
example, a 486DX2-66 has an external clock speed of 33MHz.
CPU External
Clock Speed
JP3
JP4
JP5
ID3
20MHz
OPEN
SHORT
SHORT
1-2
25MHz
SHORT
OPEN
SHORT
1-2
33MHz
SHORT
SHORT
OPEN
1-2
40MHz
OPEN
OPEN
SHORT
2-3
50MHz
OPEN
SHORT
OPEN
2-3
CPU Type Jumpers
CPU Type
JP1
JP2
JP18
486DX, 486DX2
1-2
1-2, 3-4
1-2
487SX, ODP486SX
2-3
1-2, 3-4
1-2
486SX
OPEN
2-3
1-2
Cyrix 486DLC
OPEN
2-3
2-3
Care should be taken when installing the CPU into the Pin Grid Array
(PGA) socket on the system board. Make certain that pin 1 of the CPU
chip is correctly aligned with pin 1 of CPU socket. The location of pin 1
on the CPU is denoted by a small notch.
Page 8 486MIS System Board User's Manual
