Architecture
836
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface A (EMIFA)
19.2.1 Clock Control
The EMIFA clock is output on the EMA_CLK pin and should be used when interfacing to external
memories. The EMIFA clock (EMA_CLK) does not run during device reset. When the RESET pin is
released and after the PLL controller releases the device from reset, EMA_CLK begins to oscillate at a
frequency determined by the PLL controller.
For details on clock generation and control, see the
Device Clocking
chapter.
19.2.2 EMIFA Requests
Different sources within the SoC can make requests to the EMIFA. These requests consist of accesses to
SDRAM memory, asynchronous memory, and EMIFA registers. Because the EMIFA can process only one
request at a time, a high performance crossbar switch exists within the SoC to provide prioritized requests
from the different sources to the EMIFA. The sources are:
1. CPU
2. EDMA
3. Other master peripherals
If a request is submitted from two or more sources simultaneously, the crossbar switch will forward the
highest priority request to the EMIFA first. Upon completion of a request, the crossbar switch again
evaluates the pending requests and forwards the highest priority pending request to the EMIFA.
When the EMIFA receives a request, it may or may not be immediately processed. In some cases, the
EMIFA will perform one or more auto refresh cycles before processing the request. For details on the
EMIFA's internal arbitration between performing requests and performing auto refresh cycles, see
19.2.3 Pin Descriptions
This section describes the function of each of the EMIFA pins.
Table 19-1. EMIFA Pins Used to Access Both SDRAM and Asynchronous Memories
Pins(s)
I/O
Description
EMA_D[x:0]
I/O
EMIFA data bus.
The number of available data bus pins varies among devices, see your device-specific data
manual for details.
EMA_ A[x:0]
O
EMIFA address bus.
The number of available address pins varies among devices, see your device-specific data
manual for details.
When interfacing to an SDRAM device, these pins are primarily used to provide the row and
column address to the SDRAM. The mapping from the internal program address to the external
values placed on these pins can be found in
. EMA_A[10] is also used during
the PRE command to select which banks to deactivate.
When interfacing to an asynchronous device, these pins are used in conjunction with the
EMA_BA pins to form the address that is sent to the device. The mapping from the internal
program address to the external values placed on these pins can be found in
EMA_BA[1:0]
O
EMIFA bank address.
When interfacing to an SDRAM device, these pins are used to provide the bank address inputs to
the SDRAM. The mapping from the internal program address to the external values placed on
these pins can be found in
When interfacing to an asynchronous device, these pins are used in conjunction with the EMA_A
pins to form the address that is sent to the device. The mapping from the internal program
address to the external values placed on these pins can be found in
EMA_WE_DQM[x:0]
O
Active-low byte enables.
When interfacing to SDRAM, these pins are connected to the DQM pins of the SDRAM to
individually enable/disable each of the bytes in a data access.
When interfacing to an asynchronous device, these pins are connected to byte enables. See
for details.
EMA_WE
O
Active-low write enable.
When interfacing to SDRAM, this pin is connected to the WE pin of the SDRAM and is used to
send commands to the device.
When interfacing to an asynchronous device, this pin provides a signal which is active-low during
the strobe period of an asynchronous write access cycle.