XC2200 Derivatives
System Units (Vol. 1 of 2)
Architectural Overview
User’s Manual
2-25
V2.1, 2008-08
ArchitectureX22, V1.1
In addition to the FIFO buffer, a bypass mechanism allows the introduction of high-
priority data without flushing the FIFO buffer.
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Transmit control information
For each data word to be transmitted, a 5-bit transmit control information has been
added to automatically control some transmission parameters, such as word length,
frame length, or the slave select control for the SPI protocol. The transmit control
information is generated automatically by analyzing the address where the user SW
has written the data word to be transmitted (32 input locations = 2^5 = 5 bit transmit
control information).
This feature allows individual handling of each data word, e.g. the transmit control
information associated to the data words stored in a transmit FIFO can automatically
modify the slave select outputs to select different communication targets (slave
devices) without CPU load. Alternatively, it can be used to control the frame length.
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Flexible frame length control
The number of bits to be transferred within a data frame is independent of the data
word length and can be handled in two different ways. The first option allows
automatic generation of frames up to 63 bits with a known length. The second option
supports longer frames (even unlimited length) or frames with a dynamically controlled
length.
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Interrupt capability
The events of each USIC channel can be individually routed to one of 4 service
request outputs, depending on the application needs. Furthermore, specific start and
end of frame indications are supported in addition to protocol-specific events.
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Flexible interface routing
Each USIC channel offers the choice between several possible input and output pins
connections for the communications signals. This allows a flexible assignment of
USIC signals to pins that can be changed without resetting the device.
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Input conditioning
Each input signal is handled by a programmable input conditioning stage with
programmable filtering and synchronization capability.
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Baud rate generation
Each USIC channel contains an own baud rate generator. The baud rate generation
can be based either on the internal module clock or on an external frequency input.
This structure allows data transfers with a frequency that can not be generated
internally, e.g. to synchronize several communication partners.
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Transfer trigger capability
In master mode, data transfers can be triggered events generated outside the USIC
module, e.g. at an input pin or a timer unit (transmit data validation). This feature
allows time base related data transmission.
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Debugger support
The USIC offers specific addresses to read out received data without interaction with
the FIFO buffer mechanism. This feature allows debugger accesses without the risk
of a corrupted receive data sequence.
