
Agere Systems Inc.
79
Data Sheet
July 2001
T8302 Internet Protocol Telephone
Advanced RISC Machine (
ARM
)
8 External Memory Interface (EMI)
(continued)
8.3.2 External Read
During the first cycle of the system clock, the
A[23:0]
and
BE1N
signals become valid. If
SET
(bit 7) of the corre-
sponding
chip select configuration register
is 0, the appropriate chip select (
FLASH_CS
,
CS1
,
CS2
,
CS3
) and
RDN
also go active during this cycle. If an additional cycle of address setup with respect to the chip select
RDN
is
desired, the
SET
bit can be set to 1, and the chip select and
RDN
will go active during the second cycle of the sys-
tem clock.
8.3.3 Wait-States
During an external read or write, the number of active cycles during each access is determined by the number of
wait-states (
WS[3:0]
) and
EXWAIT
pin, if it is used.
A minimum of 2 wait-states must be programmed for external reads and writes to work properly.
WS = 0000 or WS = 0001 are not valid values.
Use of the
EXWAIT
pin (for slow devices) is enabled by setting the
WT
bit (bit 8) of the appropriate
chip select
configuration register
. The polarity of the
EXWAIT
pin is programmed by the value of
WP
[bit 0] in the
options
register
(see Table 65 on page 89)
.
8.3.4 Hold State
If additional hold time is needed between the chip select going inactive and the start of the next access, one, two,
or three hold states may be added by setting
HS
(bits 5:4) of the corresponding
chip select configuration regis-
ter
to the appropriate value.
8.3.5 Hold Disable
For multiaccess read transactions to a device that requires hold states, it is only necessary to have hold states at
the end of the last access and not on each intermediate access. These intermediate hold states are suppressed by
setting
HD
(bit 10) of the appropriate
chip select configuration register
.
8.3.6 Error Conditions
The following errors are recorded in the
status register
(see Table 64 on page 88)
:
I
MAC register error. If an attempt is made to read/write the
Ethernet MAC registers
in the
0xE001 0800:0xE001 FFFF range when the PHY is not active (i.e., when the MAC is not receiving its
Tx/Rx
clocks), a
MAC register
error occurs, and is recorded in
MACRE
(bit 15) of the
status register
.
I
Alignment error. If a nonaligned word access (with address bits 1:0 being nonzero) or a nonaligned half-word
access (with address bit 0 being nonzero) is attempted, an alignment error occurs and is recorded in
AE
(bit 13)
of the
status register
.
I
Peripheral subword access error. If a half-word or byte access attempt is made to the peripheral address space
(0xE000 0000:0xEFFF FFFF), a peripheral subword access error occurs, and is recorded in
PSWE
(bit 12) of
the
status register
.
I
Peripheral code access error. If an opcode fetch is attempted from peripheral address space
(0xE000 0000:0xEFFF FFFF), a peripheral code access error occurs and is recorded in the
PCAE
bit (bit 10) of
the
status register
.
I
DCC read error. If the
ARM
processor/DMA controller attempts to read from the
ARM
2DSP data buffer
(0xE004 0000:0xE004 07FF), a DCC read error occurs and is recorded in the
DCCRE
bit (bit 9) of the
status
register
.