C161U
System Reset
Preliminary Data Sheet
370
02.2000
PRELIMINARY
PRE
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The configuration via P0H is latched in register RP0H for subsequent evaluation by
software. Register RP0H is described in chapter “The External Bus Interface”.
The following describes the different selections that are offered for reset configuration. The default
modes refer to pins at high level, ie. without external pulldown devices connected. Please also
consider the note (above) on reserved pins.
Adapt Mode
Pin P0L.1 (ADP) selects the Adapt Mode, when low during reset. In this mode the C161U
goes into a passive state, which is similar to its state during reset. The pins of the C161U
float to tristate or are deactivated via internal pullup/pulldown devices, as described for
the reset state. In addition also the RSTOUT pin floats to tristate rather than be driven
low, and the on-chip oscillator is switched off.
This mode allows switching a C161U that is mounted to a board virtually off, so an
emulator may control the board’s circuitry, even though the original C161U remains in its
place. The original C161U also may resume to control the board after a reset sequence
with P0L.1 high.
Default: Adapt Mode is off.
Bootstrap Loader Mode
Pin P0L.4 (BSL) activates the on-chip bootstrap loader, when low during reset. The
bootstrap loader allows moving the start code into the internal RAM of the C161U via the
serial interface ASC. The C161U will remain in bootstrap loader mode until a hardware
reset with P0L.4 high or a software reset.
Default: The C161U starts fetching code from location 00’0000
H, the bootstrap loader is
off.
External Bus Type
Pins P0L.7 and P0L.6 (BUSTYP) select the external bus type during reset, if an external
start is selected via pin EA. This allows the configuration of the external bus interface of
the C161U even for the first code fetch after reset. The two bits are copied into bit field
BTYP of register BUSCON0. P0L.7 controls the data bus width, while P0L.6 controls the
address output (multiplexed or demultiplexed). This bit field may be changed via
software after reset, if required.
BTYP Encoding External Data Bus Width
External Address Bus Mode
0 0
8-bit Data
Demultiplexed Addresses
0 1
8-bit Data
Multiplexed Addresses