Conventions that this book can use are described in:


The typographical conventions are:


Highlights important notes, introduces special terminology, denotes internal cross-references, and citations.


Highlights interface elements, such as menu names. Denotes signal names. Also used for terms in descriptive lists, where appropriate.


Denotes text that you can enter at the keyboard, such as commands, file and program names, and source code.


Denotes a permitted abbreviation for a command or option. You can enter the underlined text instead of the full command or option name.

monospace italic

Denotes arguments to monospace text where the argument is to be replaced by a specific value.

monospace bold

Denotes language keywords when used outside example code.

< and >

Enclose replaceable terms for assembler syntax where they appear in code or code fragments. For example:

MRC p15, 0 <Rd>, <CRn>, <CRm>, <Opcode_2>

Timing diagrams

The figure named Figure 1 explains the components used in timing diagrams. Variations, when they occur, have clear labels. You must not assume any timing information that is not explicit in the diagrams.

Shaded bus and signal areas are undefined, so the bus or signal can assume any value within the shaded area at that time. The actual level is unimportant and does not affect normal operation.

Figure 1. Key to timing diagram conventions

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The signal conventions are:

Signal level

The level of an asserted signal depends on whether the signal is active-HIGH or active-LOW. Asserted means:

  • HIGH for active-HIGH signals

  • LOW for active-LOW signals.

Lower-case n

At the start or end of a signal name denotes an active-LOW signal.

Copyright © 2007, 2009-2010 ARM Limited. All rights reserved.ARM DDI 0418E