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EMIFA
Memory
Controller
Registers
State
Machine
MOD_G_RST
EMIFA
PSC
CHIP_RST
Hard Reset
from PLL
Architecture
869
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface A (EMIFA)
19.2.6 Data Bus Parking
The EMIFA always drives the data bus to the previous write data value when it is idle. This feature is
called data bus parking. Only when the EMIFA issues a read command to the external memory does it
stop driving the data bus. The data bus is released (tri-stated) when the chip enable (EMA_CS[n]) is
asserted by EMIFA for the read access. After the read operation is completed, the data bus is driven
again by the bus parking feature at the end of the turnaround time. At all other times that the EMIF is
enabled but not actively transferring data, the bus parking feature drives the data bus to the last written
value.
The one exception to this behavior occurs after performing an asynchronous read operation while the
EMIFA is in the self-refresh state. In this situation, the read operation is not followed by the EMIFA parking
the data bus. Instead, the EMIFA tri-states the data bus. Therefore, it is not recommended to perform
asynchronous read operations while the EMIFA is in the self-refresh state, in order to prevent floating
inputs on the data bus. External pull-ups, such as 10k
Ω
resistors, should be placed on the 16 EMIFA data
bus pins (which do not have internal pull-ups) if it is required to perform reads in this situation. The precise
resistor value should be chosen so that the worst case combined off-state leakage currents do not cause
the voltage levels on the associated pins to drop below the high-level input voltage requirement.
For information about the self-refresh state, see
19.2.7 Reset and Initialization Considerations
The EMIFA memory controller has two reset signals, CHIP_RST and MOD_G_RST. The CHIP_RST is a
module-level reset that resets both the state machine as well as the EMIFA memory controller's memory-
mapped registers. The MOD_G_RST resets the state machine only. If the EMIFA memory controller is
reset independently of other peripherals, the user's software should not perform memory, as well as
register accesses, while CHIP_RST or MOD_G_RST are asserted. If memory or register accesses are
performed while the EMIFA memory controller is in the reset state, other masters may hang. Following the
rising edge of CHIP_RST or MOD_G_RST, the EMIFA memory controller immediately begins its
initialization sequence. Command and data stored in the EMIFA memory controller FIFOs are lost.
describes the different methods for asserting each reset signal.
shows the
EMIFA memory controller reset diagram.
Table 19-24. Reset Sources
Reset Signal
Reset Source
CHIP_RST
Hardware/ Device Reset
MOD_G_RST
Power and Sleep Controller
Figure 19-16. EMIFA Reset Block Diagram