Preliminary
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Use Cases And Tips
5.4.1.4
GPMC Configuration for Asynchronous Read Access
The clock runs at 104 MHz ( f = 104 MHz; T = 9, 615 ns).
shows the timing parameters (on the memory side) that determine the parameters on the
GPMC side.
shows how to calculate timings for the GPMC using the memory parameters.
shows the asynchronous read access.
Table 5-48. AC Characteristics for Asynchronous Read Access
AC Read Characteristics
Description
Duration (ns)
on the Memory Side
tCE
Read Access time from CS low
80
tAAVDS
Address setup time to rising edge of ADV
3
tAVDP
ADV low time
6
tCAS
CS setup time to ADV
0
tOE
Output enable to output valid
6
tOEZ
Output enable to High-Impedance
7
Use the following formula to calculate the RdCycleTime parameter for this typical access:
RdCycleTime = RdAcce AccessCompletion = RdAcce 1 clock cycle + tOEZ
•
First, on the memory side, the external memory makes the data available to the output bus. This is
the memory-side read access time defined in
: the number of clock cycles between the
address capture (ADV rising edge) and the data valid on the output bus.
The GPMC requires some hold time to allow the data to be captured correctly and the access to be
finished.
•
To read the data correctly, the GPMC must be configure to meet the data setup time requirement of
the memory; the GPMC module captures the data on the next rising edge. This is access time on
the GPMC side.
•
There must also be a data hold time for correctly reading the data (checking that there is no OE/CS
deassertion while reading the data). This data hold time is 1 clock cycle (that is, Acce 1).
•
To complete the access, OE/CS signals are driven to high-impedance. Acce 1 + tOEZ is
the read cycle time.
•
Addresses can now be relatched and a new read cycle begun.
655
SPRUGX9 – 15 April 2011
General-Purpose Memory Controller (GPMC)
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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