TC1767
Introduction
2.1.3
Reserved, Undefined, and Unimplemented Terminology
In tables where register bit fields are defined, the following conventions are used to
indicate undefined and unimplemented function. Furthermore, types of bits and bit fields
are defined using the abbreviations as shown in Table 2.
Table 2
Bit Function Terminology
Function of Bits
Description
Unimplemented,
Reserved
Register bit fields named 0 indicate unimplemented functions
with the following behavior.
• Reading these bit fields returns 0.
• These bit fields should be written with 0 if the bit field is
defined as r or rh.
• These bit fields have to be written with 0 if the bit field is
defined as rw.
These bit fields are reserved. The detailed description of these
bit fields can be found in the register descriptions.
rw
rwh
r
The bit or bit field can be read and written.
As rw, but bit or bit field can be also set or reset by hardware.
The bit or bit field can only be read (read-only).
w
The bit or bit field can only be written (write-only). A read to this
register will always give a default value back.
rh
s
This bit or bit field can be modified by hardware (read-hardware,
typical example: status flags). A read of this bit or bit field give
the actual status of this bit or bit field back. Writing to this bit or
bit field has no effect to the setting of this bit or bit field.
Bits with this attribute are “sticky” in one direction. If their reset
value is once overwritten by software, they can be switched
again into their reset state only by a reset operation. Software
cannot switch this type of bit into its reset state by writing the
register. This attribute can be combined to “rws” or “rwhs”.
f
Bits with this attribute are readable only when they are accessed
by an instruction fetch. Normal data read operations will return
other values.
2.1.4
Register Access Modes
Read and write access to registers and memory locations are sometimes restricted. In
memory and register access tables, the terms as defined in Table 3 are used.
Data Sheet
9
V1.3, 2009-09
INFINEON [ Infineon ]
