
C165UTAH
Architectural Overview
Data Sheet
36
2001-02-23
way. For up to five address areas the bus mode (multiplexed / demultiplexed), the data
bus width (8-bit / 16-bit) and even the length of a bus cycle (waitstates, signal delays)
can be selected independently. This allows to access a variety of memory and peripheral
components directly and with maximum efficiency. If the device does not run in Single
Chip Mode, where no external memory is required, the EBC can control external
accesses in one of the following four different external access modes:
16-/18-/20-/24-bit Addresses, 16-bit Data, Demultiplexed
16-/18-/20-/24-bit Addresses, 8-bit Data, Demultiplexed
16-/18-/20-/24-bit Addresses, 16-bit Data, Multiplexed
16-/18-/20-/24-bit Addresses, 8-bit Data, Multiplexed
The demultiplexed bus modes use PORT1 for addresses and PORT0 for data input/
output. The multiplexed bus modes use PORT0 for both addresses and data input/
output. All modes use Port 4 for the upper address lines (A16...) if selected.
Important timing characteristics of the external bus interface (waitstates, ALE length and
Read/Write Delay) have been made programmable to allow the user the adaption of a
wide range of different types of memories and/or peripherals. Access to very slow
memories or peripherals is supported via a particular 'Ready' function.
For applications which require less than 64 KBytes of address space, a non-segmented
memory model can be selected, where all locations can be addressed by 16 bits, and
thus Port 4 is not needed as an output for the upper address bits (A22/A19/A17...A16),
as is the case when using the segmented memory model.
The
on-chip XBUS
is an internal representation of the external bus and allows to access
integrated application-specific peripherals/modules in the same way as external
components. It provides a defined interface for these customized peripherals.
3.3
Clock Generation Concept
The on-chip clock generator provides the C165UTAH with its basic clock signal that
controls all activities of the controller hardware. Its oscillator can either run with an
external crystal and appropriate oscillator circuitry (see also recommendations in
chapter Dedicated Pins“) or it can be driven by an external oscillator. The oscillator
either directly feeds the external clock signal to the controller hardware (through buffers),
divides the external clock frequency by 2 or 4, or feeds an on-chip phase locked loop
(PLL) which multiplies the input frequency by a selectable factor
F
. This resulting internal
clock signal is also referred to as “CPU clock”. Two separated clock signals are
generated for the CPU itself and the peripheral part of the chip. While the CPU clock is
stopped during the idle mode, the peripheral clock keeps running. Both clocks are
switched off, when the power down mode is entered.