
ARM940T Signal Descriptions
A-2
Copyright 199, 2000 ARM Limited. All rights reserved.
ARM DDI 0144B
A.1
AMBA signals
Table A-1 on page A-2 describes the AMBA signals used by the ARM940T.
Table A-1 AMBA signals
Name
Direction
Description
AGNT
Input
Bus grant. A signal from the bus arbiter to a bus master that indicates the bus master
is granted the bus when
BWAIT
next goes LOW.
AREQ
Output
Bus request. A signal from the bus master to the bus arbiter that indicates that the
ARM940T requires the bus.
ASTB
Output
Indicates a non-idle A-TRAN cycle.
BA[31:0]
Output
Address bus. The processor address bus driven by the active bus master.
BCLK
Input
Bus clock. This clock times all bus transfers. Both the LOW phase and HIGH phase
of
BCLK
are used to control transfers on the bus.
BD[31:0]
Input/Output
Data bus. This is a bidirectional system data bus.
BERROR
Input/Output
Error response. A transfer error is indicated by the selected bus slave using the
BERROR
signal. When
BERROR
is HIGH, a transfer error has occurred, when
BERROR
is LOW, the transfer is successful. This signal is also used in combination
with the
BLAST
signal to indicate a bus retract operation.
BLAST
Input/Output
Last response. This signal is driven by the selected bus slave to indicate if the current
transfer is the last of a burst sequence. When
BLAST
is HIGH, the decoder must
allow sufficient time for address decoding. When
BLAST
is LOW, the next transfer
can continue a burst sequence.
BLOK
Output
Locked transfers. When HIGH, this signal indicates that the current transfer, and the
next transfer, are to be indivisible, and that no other bus master must be given access
to the bus. This signal is used by the bus arbiter.
BnRES
Input
Reset. The bus reset signal is active LOW, and is used to reset the system and the bus.
This is the only active LOW AMBA signal.
BUFFSTRAHB
Output
When HIGH, indicates that a buffered write is in progress and that
NCMAHB
is not
valid.
BPROT[1:0]
Output
Protection control.These signals provide additional information about a bus access
and are primarily intended for use by a bus decoder when acting as a basic protection
unit. The signals indicate if the transfer is an opcode fetch or data access. The signals
also indicate if it is a privileged mode or User mode transfer.