Data Sheet
June 2001
DSP16410B Digital Signal Processor
102
Agere Systems—Proprietary
Use pursuant to Company instructions
Agere Systems Inc.
4 Hardware Architecture
(continued)
4.14 System and External Memory Interface (SEMI)
(continued)
4.14.1 External Interface
(continued)
4.14.1.2 Asynchronous Memory Bus Arbitration
The SEMI allows an external device to request direct access to an asynchronous external memory by asserting the
EREQN pin. The SEMI acknowledges the external request by asserting its EACKN pin. The SEMI allows an exter-
nal device to extend the duration of an external asynchronous access by deasserting the ERDY pin.
Table 53. Asynchronous Memory Bus Arbitration Pins
Pin
Description
EREQN
(negative-
assertion input)
An external device asserts EREQN (low) to request direct access to an asynchronous external 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 performing the follow-
ing:
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 continues 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 relinquishes 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
after 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.
The SEMI acknowledges the request of an external device for direct access to an asynchronous external
memory by asserting EACKN. See the description of the EREQN pin above for details. The software can
read the state of the EACKN pin in the EACKN field (
ECON1
[5]—see
Table 60 on page 110
).
An external device instructs the SEMI to extend the duration of the current asynchronous external memory
access by driving ERDY low. See
Section 4.14.5.2
for details. The software can read the state of the ERDY
pin in the EREADY field (
ECON1
[6]—see
Table 60 on page 110
).
ATIME
MAX
is the greatest of IATIME(
ECON0
[11:8]), YATIME (
ECON0
[7:4]), and XATIME (
ECON0
[3:0]).
EACKN
(negative-
assertion output)
ERDY
(positive-
assertion input)
Note:
If this pin is not in use by the application or if all external memory is synchronous, ERDY must be tied
high.