82C836 Datasheet, PDF (29/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT

Section 3
Functional Description
Configuration Registers
The 82C836 contains an extensive and versatile set of internal configuration registers
(ICRs) for enabling or disabling various optional modes and features. The internal
configuration registers are accessed using I/O ports 22H and 23H. To read or write an
internal configuration register, the register number (index) should be output to port 22H,
and the contents of the register then read or written at port 23H. Each read or write to
port 23H must be preceded by an output to port 22H, even if the index value written to
port 22H is unchanged from the last access.
Reset Strap Options
The 82C836 features reset strap options without having to use extra pins. The 82C836
uses -DACK lines to implement the strap options. The -DACK lines are normally
outputs, but during power-up they are used as input signals. These lines are sampled
during the high state of XRST after PWRGOOD goes high. Later, they convert to
outputs for normal functions. A 4.7K ohm pull-down or pull-up resistor pulls the signals
low or high for strap option sampling. Table 3-1 describes the pins used for strap
options. Figure 3-1 shows an alternate way to implement a pull-low function in cases
where a simple pull-down resistor is not suitable because of signal loading.
Note: The circuit shown in Figure 3-1 should not be used in systems using Standby Refresh
in MRA mode.
Chips and Technologies, Inc.
PRELIMINARY
Revision 3.0 3-1