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2.3 Signal Descriptions
Table 1 describes the function of each of the EMIF pins.
Table 1. EMIF Pins
Pins(s) I/O Description
EM_ A[22:0] O EMIF address bus. These pins are used in conjunction with the EM_BA pins to form the address that is
sent to the device.
EM_BA[1:0] O EMIF bank address. These pins are used in conjunction with the EM_A pins to form the address that is
sent to the device.
EM_CS[5:2] O Active-low chip enable pin for asynchronous devices. These pins are meant to be connected to the
chip-select pin of the attached asynchronous device.
EM_D[15:0] I/O EMIF data bus.
EM_RW O Read/Write select pin. This pin is high for the duration of an asynchronous read access cycle and low
for the duration of an asynchronous write cycle.
EM_OE O Active-low pin enable for asynchronous devices. This pin provides a signal which is active-low during
the strobe period of an asynchronous read access cycle.
EM_WE O Active-low write enable. This pin provides a signal which is active-low during the strobe period of an
asynchronous write access cycle.
EM_WAIT[5:2] I Wait input with programmable polarity. A connected asynchronous device can extend the strobe period
of an access cycle by asserting the WAIT input to the EMIF as described in Section 2.5.8. To enable
this functionality, the EW bit in the asynchronous configuration register (ACFGn) must be set to 1. In
addition, the WPn bit in the asynchronous wait cycle configuration register (AWCCR) must be
configured to define the polarity of the EM_WAITn pin.
2.4 Pin Multiplexing
The EMIF pins are multiplexed with other peripherals such as PCI, HPI, GPIO, and ATA. See the
device-specific data manual for instructions on how to select the EMIF pins for proper operation.
2.5 Asynchronous Controller and Interface
The EMIF easily interfaces to a variety of asynchronous devices including Flash and ASRAM. It can be
operated in three major modes:
• Normal mode
• Select Strobe (SS) mode
• NAND Flash mode
The behavior of the EM_CS signal is the single difference between Normal mode and Select Strobe mode
(see Table 2). In Normal mode, the EM_CS signal becomes active at the beginning of the setup period
and remains active for the duration of the transfer. In Select Strobe mode, the EM_CS signal functions as
a strobe signal, active only during the strobe period of an access.
In NAND Flash mode, the EMIF hardware is able to calculate the error correction code (ECC) for each
512 byte data transfer. In addition to the three modes of operation, the EMIF also provides configurable
cycle timing parameters and an Extended Wait mode that allows the connected device to extend the
strobe period of an access cycle. The following sections describe the features related to interfacing with
external asynchronous devices.
Table 2. Behavior of EM_CS Signal Between Normal Mode and
Select Strobe Mode
Mode Operation of EM_CS[5:2]
Normal Active during the entire asynchronous access cycle
Select Strobe Active only during the strobe period of an access cycle
10
Asynchronous External Memory Interface (EMIF) SPRUEQ7C–February 2010
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