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9.1
External Memory Interface (EMIFA)
9.1.1
Configuration of EMIFA
9.1.2
System Implementation of EMIFA
Peripheral Section
pull-downs are not included normally pins can still be floated with no functional issues for the device.
However, this normally does cause additional leakage currents which can be eliminated if external pull-ups
or pull-downs are used. When pull-ups or pull-downs are used the leakage current is approximately 100uA
per pin. When the pins are floating the leakage can be several milliamps. Although the recommendations
normally indicate using external pull-up resistors, pulll-down resistors can also be used. The leakage is the
same whether pull-ups or pull-downs are used. Connections directly to power or ground can be used only
if the pins can be guaranteed to never be configured as outputs. Use of boundary scan normally drives all
signals as outputs so direct connections to power or ground are not recommended if boundary scan is
used.
If a peripheral is selected (via the configuration strapping) but not enabled (via the peripheral configuration
register), then the I/Os can be treated the same as if the peripheral was not selected.
Documentation for EMIFA:
•
TCI648x DSP External Memory Interface (EMIF) Reference Guide (SPRU925)
•
TCI6482 System Boot
•
TCI6482 IBIS Model File
•
Using IBIS Modes for Timing Analysis (
SPRA839
)
The EMIFA peripheral can be disabled using boot strapping options, as defined in the TCI6482 data
manual. If the EMIFA is enabled via boot strapping, it still needs to be enabled via software after a reset.
The clock to be used for EMIFA can either be supplied externally to the AECLKIN pin or can be generated
internally from the CPU core clock. The internally generated clock is referred to as SYSCLK4. After a
reset, SYSCLK4 is CPU core clock / 8. The SYSCLK4 divider can be changed via software register
accesses to PLL1.
If the EMIFA peripheral is not used, most EMIFA inputs can be left unconnected. Internal pull-up and
pull-down resistors are included on this interface so leakage will be minimal. Some EMIFA signals are
used for boot stapping options that are latched on the rising edge of POR (cold boot) or rising edge of
RESET (warm boot). If these signals are connected to other components it is recommnended to have 1K
pull-up or pull-down resistors in order to make sure the boot strapping options are properly latched.
If only a portion of the peripheral is used, control pins that are not used should be pulled to a valid state
and data pins that are not used can be left floating.
One of the boot modes is Boot over EMIF. In this mode, after reset the DSP immediately begins executing
from the base address of CE3 in 8-bit asynchronous mode.
Note that all synchronous memories connected to the EMIF should have clock enable low during device
power ramp and reset to avoid any inadvertent clocking of memories during power ramp and reset low.
This can be done by having a weak pull-down resistor (i.e. 10K) on the CKE signals.
Generally, series resistors should be used on the EMIFA signals to reduce over-shoot and under-shoot.
Generally acceptable values are 10, 22 or 33 ohms. To determine the optimum value simulations using
the IBIS models should be performed to check for signal integrity and AC timings.
Significant signal degradation can occur when multiple devices are connected on the EMIFA. Simulations
are the best mechanism for determining the best physical topologies and the highest frequency obtainable
with that topology. Generally, a synchronous interface is best from a performance standpoint and an
asynchronous interface has less performance but is easier to implement.
SPRAAC7B – April 2006
TMS320TCI6482 Design Guide and Migration from TMS320TCI100
23
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