Hardware Reference
In-Depth Information
Photo 2.7 Motherboard with ISA/EISA bus connectors (note that two out of
the eight slots only provide access to the 8-bit bus)
Photo 2.8 Motherboard with ISA/EISA slots and PCI (CCA) combined slots
Electrical characteristics
All of the signal lines present on the expansion connector(s) are TTL compatible.
In the case of output signals from the system motherboard, the maximum loading
imposed by an expansion card adapter should be limited to no more than two
low-power (LS) TTL devices. The following expansion bus lines are open-
collector: /MEMCSI6, /IOCS16, and 0WS. Note that the '/' indicates that the
signal in question is active low (or asserted low ).
The /IOCHRDY line is available for interfacing slow memory or I/O devices.
Normal processor generated read and write cycles use four clock (CLK) cycles
per byte transferred. The standard PC clock frequency of 4.77 MHz results in a
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