ISA Bus. Part III

With the standard frequency of PCI-bus equal to 33 MHz, the value “PCICLK/4” ensures the standard frequency of ISA-bus. But as most ISA-devices are able to operate with much higher frequency, the value “OCICLK/3” can be used for this parameter. This value sets the frequency 11 MHz for ISA-bus. Such transition like any other increase of frequency causes the enhanced heat transition by the appropriate devices In case of poor heat exchange, such procedure may cause overheated elements of ISA-device and its failure. It is not recommended to increase frequency while using the disk controllers as ISA-devices. It is clear that if the frequency of PCI-bus is changed, for example during processor overclocking, the frequency of ISA-bus is also changed.

The parameter “ISA Bus Clock” or similar to it may have the following values: PCI/x, PCICLK/x, CLK/x where x – a number ranging from 2 to 12 (2, 3, 4, 5, 6, 8, 10 and 12). The fixed values, for example 7.159 MHz, or the value “Auto” (indicates the automatic selection of frequency by a system) can also be used.