P R E L I M I N A R Y
the defaults for the PIOs. The system initialization code
PROGRAMMABLE I/O (PIO) PINS
must reconfigure the PIOs as required.
There are 32 pins on the Am186ES and Am188ES mi-
crocontrollers that are available as user-programmable
I/O signals. Table 2 on page 34 and Table 3 on
page 34 list the PIO pins. Each of these pins can be
used as a user-programmable input or output signal if
the normal shared function is not needed.
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.
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.
Note that emulators use A19, A18, A17, S6, and UZI.
In environments where an emulator is needed, these
pins must be configured for normal function—not as
PIOs.
If the AD15–AD0 bus override is enabled on power-on
reset, then S6/CLKDIV2 and UZI revert to normal oper-
ation 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.
After power-on reset, the PIO pins default to various
configurations. The column titled Power-On Reset Sta-
tus in Table 2 on page 34 and Table 3 on page 34 lists
52
Am186/188ES and Am186/188ESLV Microcontrollers
AMD [ AMD ]
