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Hardware Description
18
which improves microcontroller performance. The DMAC supports single transfer and
chained buffer transfer. In chained buffer transfer mode, the address is automatically
incremented, when the countable limit of the current transfer buffer is reached.
To launch a transfer, the peripheral triggers its associated DMA channels by using
transmit and receive signals. When the programmed data is transferred, an end of transfer
interrupt is generated by the peripheral itself. There are four kinds of interrupts generated
by the DMAC:
• Buffer Transfer Completed
• Chained Buffer Transfer Completed
• Access Error
• Descriptor Integrity Check Error
5.17. Debug Unit (DBGU)
The Debug Unit is a simple UART which provides only RX/TX lines. It is used as a simple
serial console for Firmware and Operating Systems.
5.18. JTAG Unit
The JTAG unit can be used for hardware diagnostics, hardware initialization, flash memory
programming, and debug purposes. The JTAG unit supports two different modes, namely
the "ICE Mode", and the "Boundary Scan" mode. It is normally jumpered for "ICE Mode".
JTAG interface devices are available for the unit. However, the use of them is not within
the scope of this document.
5.19. Two-wire Interface (TWI)
The StampA5D3x features three two-wire interfaces.
The TWI is also known under the expression "I
2
C-Bus", which is a trademark of Philips
and may therefore not be used by other manufacturers. However, interoperability is
guaranteed. The TWI supports both master or slave mode.
The TWI uses only two lines, namely serial data (SDA) and serial clock (SCL). According to
the standard, the TWI clock rate is limited to 400 kHz in fast mode and 100 kHz in normal
mode, but configurable baud rate generator permits the output data rate to be adapted
to a wide range of core clock frequencies.
5.20. Multimedia Card Interface (MCI)
The StampA5D3x features a onboard Micro-SD-Card slot, which is connected to the
HMCI1 interface of the microcontroller. The HMCI0 interface is provided for external
additional use.