Table 3-5 Ntrans Encoding - ARM ARM7TDMI Technical Reference Manual

3.4.5 nTRANS
3.4.6 LOCK
3.4.7 TBIT
ARM DDI 0210C
The nTRANS output conveys information about the transfer. An MMU can use this
signal to determine whether an access is from a privileged mode or User mode. This
signal can be used with nOPC to implement an access permission scheme. The
meaning of nTRANS is listed in Table 3-5.
More information relevant to the nTRANS signal and security is provided in Privileged
mode access on page 3-31.
LOCK is used to indicate to an arbiter that an atomic operation is being performed on
the bus. LOCK is normally LOW, but is set HIGH to indicate that a SWP or SWPB
instruction is being performed. These instructions perform an atomic read/write
operation, and can be used to implement semaphores.
TBIT is used to indicate the operating state of the ARM7TDMI processor. When in:
• ARM state, the TBIT signal is LOW
• Thumb state, the TBIT signal is HIGH.
Note
Memory systems do not usually have to use TBIT because MAS[1:0] indicates the size
of the instruction required.
Copyright © 2001, 2004 ARM Limited. All rights reserved.

Table 3-5 nTRANS encoding

nTRANS Mode
0 User
1 Privileged
Memory Interface
3-13