P R E L I M I N A R Y
PROGRAMMABLE I/O (PIO) PINS
There are 32 pins on the Am186EM and Am188EM mi-
crocontrollers that are available as user multipurpose
signals. Table 2 and Table 3 on page 30 list the PIO
pins. Each of these pins can be used as a user-pro-
grammable input or output signal if the normal shared
function is not needed.
If a pin is enabled to function as a PIO signal, the pre-
assigned signal function is disabled and does not affect
the level on the pin. A PIO signal can be configured to
operate as an input or output with or without a weak
pullup or pulldown, or as an open-drain output.
After power-on reset, the PIO pins default to various
configurations. The column titled Power-On Reset Sta-
tus in Table 2 and Table 3 on page 30 lists the defaults for
the PIOs. The system initialization code must reconfigure
the PIOs as required.
The A19–A17 address pins default to normal operation
on power-on reset, allowing the processor to correctly
begin fetching instructions at the boot address
FFFF0h. The DT/R, DEN, and SRDY pins also default to
normal operation on power-on reset.
Note that emulators use A19, A18, A17, S6, and UZI.
If the AD15–AD0 bus override is enabled on power-on
reset, then S6/CLKDIV2 and UZI revert to normal opera-
tion instead of PIO input with pullup. If BHE/ADEN (186)
or RFSH2/ADEN (188) is held Low during power-on reset
the AD15–AD0 bus override is enabled.
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Am186/188EM and Am186/188EMLV Microcontrollers
AMD [ AMD ]
