
Data Sheet
June 2001
DSP16410B Digital Signal Processor
Agere Systems Inc.
Agere Systems—Proprietary
Use pursuant to Company instructions
259
8 Signal Descriptions
(continued)
8.3 System and External Memory
Interface
(continued)
EROMN—EROM Space Enable:
Negative-assertion
output. The external ROM enable selects the EROM
memory component (external program memory). For
asynchronous accesses, the SEMI asserts EROMN for
the number of cycles specified by the XATIME[3:0] field
(
ECON0
[3:0]—see
Table 59 on page 109
). For syn-
chronous accesses, the SEMI asserts EROMN for two
instruction cycles (one ECKO cycle
2
). EROM is config-
ured as synchronous if the ERTYPE pin is high. The
SEMI 3-states EROMN if it grants a request by an
external device to access the external memory (see
description of the EREQN pin).
EION—EIO Space Enable:
Negative-assertion output.
The external I/O enable selects the EIO memory com-
ponent (external memory-mapped peripherals or data
memory). For asynchronous accesses, the SEMI
asserts EION for the number of cycles specified by the
IATIME[3:0] field (
ECON0
[11:8]—see
Table 59 on
page 109
). For synchronous accesses, the SEMI
asserts EION for two instruction cycles (one ECKO
cycle
1
). EION is configured as synchronous if the
ITYPE field is set (
ECON1
[10]—see
Table 60 on
page 110
) is set. The SEMI 3-states EION if it grants a
request by an external device to access the external
memory (see description of the EREQN pin).
ERDY—External Device Ready for SEMI Data:
Posi-
tive-assertion input. The external READY input is a
control pin that allows an external device to extend an
external asynchronous memory access. If driven low
by the external device, the SEMI extends the current
external memory access that is already in progress. To
guarantee proper operation, ERDY must be driven low
at least 4 CLK cycles before the end of the access and
the enable must be programmed for at least 5 CLK
cycles of assertion (via the YATIME, XATIME, or
IATIME field of
ECON0
—see
Table 59 on page 109
).
The SEMI ignores the state of ERDY prior to 4 CLK
cycles before the end of the access. The access is
extended by 4 CLK cycles after ERDY is driven high.
The state of ERDY is readable in the EREADY field
(
ECON1
[6]—see
Table 60 on page 110
.
Note:
If ERDY is not in use by the application or if all
external memory is synchronous, ERDY must be
tied high.
EREQN—External Device Requests Access to
SEMI Bus:
Negative-assertion input. An external
device asserts EREQN low to request the external
memory bus for access to external asynchronous
memory. If the NOSHARE field (
ECON1
[8]—see
Table 60 on page 110
) is set, the DSP16410B ignores
the request. If NOSHARE is cleared, a minimum of
four cycles later the SEMI grants the request by per-
forming the following:
First, the SEMI completes any external access that is
already in progress.
The SEMI 3-states the address bus and segment
address (EA[18:0] and ESEG[3:0]), the data bus
(ED[31:0]), and all the external enables and strobes
(ERAMN, EROMN, EION, and ERWN[1:0]) until the
external device deasserts EREQN. The SEMI con-
tinues to drive ECKO.
The SEMI acknowledges the request by asserting
EACKN.
The cores and the DMAU continue processing. If a
core or the DMAU attempts to perform an external
memory access, it stalls until the external device relin-
quishes the bus. If the external device deasserts
EREQN (changes EREQN from 0 to 1), four cycles
later the SEMI deasserts EACKN (changes EACKN
from 0 to 1). To avoid external bus contention, the
external device must wait for at least ATIME
MAX
cycles
2
after the it deasserts EREQN (changes EREQN from 0
to 1) before reasserting EREQN (changing EREQN
from 1 to 0). The software can read the state of the
EREQN pin in the EREQN field (
ECON1
[4]—see
Table 60 on page 110
).
Note:
If EREQN is not in use by the application, it must
be tied high.
1. If any memory component is configured as synchronous, ECKO must be programmed as CLK/2, i.e., the ECKO[1:0] field
(
ECON1
[1:0]—
Table 60 on page 110
) must be programmed to 0x0.
2. ATIME
MAX
is the greatest of IATIME(
ECON0
[11:8]), YATIME (
ECON0
[7:4]), and XATIME (
ECON0
[3:0]).