T32UC3L0128_14 Datasheet, PDF (774/852 Pages) ATMEL Corporation – Compact Single-cycle RISC Instruction Set Including DSP Instructions

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31.6 aWire Debug Interface (AW)
Rev.: 2.3.0.1
31.6.1 Features
• Single pin debug system.
• Half Duplex asynchronous communication (UART compatible).
• Full duplex mode for direct UART connection.
• Compatible with JTAG functionality, except boundary scan.
• Failsafe packet-oriented protocol.
• Read and write on-chip memory and program on-chip flash and fuses through SAB interface.
• On-Chip Debug access through SAB interface.
• Asynchronous receiver or transmitter when the aWire system is not used for debugging.
31.6.2 Overview
The aWire Debug Interface (AW) offers a single pin debug solution that is fully compatible with
the functionality offered by the JTAG interface, except boundary scan. This functionality includes
memory access, programming capabilities, and On-Chip Debug access.
Figure 31-8 on page 775 shows how the AW is connected in a 32-bit AVR device. The
RESET_N pin is used both as reset and debug pin. A special sequence on RESET_N is needed
to block the normal reset functionality and enable the AW.
The Service Access Bus (SAB) interface contains address and data registers for the Service
Access Bus, which gives access to On-Chip Debug, programming, and other functions in the
device. The SAB offers several modes of access to the address and data registers, as dis-
cussed in Section 31.6.6.8.
Section 31.6.7 lists the supported aWire commands and responses, with references to the
description in this document.
If the AW is not used for debugging, the aWire UART can be used by the user to send or receive
data with one stop bit, eight data bits, no parity bits, and one stop bit. This can be controlled
through the aWire user interface.
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