EMIF_CLK
EMIF_nCS[n]
EMIF_nDQM
EMIF_A/EMIF_BA
EMIF_D
EMIF_nOE
EMIF_nWE
Setup
Strobe
Hold
2
3
2
Byte enables
Address
Data
EMIF Module Architecture
821
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
External Memory Interface (EMIF)
Figure 21-13. Timing Waveform of an Asynchronous Write Cycle in Select Strobe Mode
21.2.6.6 Extended Wait Mode and the EMIF_nWAIT Pin
The EMIF supports the Extend Wait Mode. This is a mode in which the external asynchronous device may
assert control over the length of the strobe period. The Extended Wait Mode can be entered by setting the
EW bit in the asynchronous
n
configuration register (CE
n
CFG) (
n
= 2, 3, or 4). When this bit is set, the
EMIF monitors the EMIF_nWAIT pin to determine if the attached device wishes to extend the strobe
period of the current access cycle beyond the programmed number of clock cycles.
When the EMIF detects that the EMIF_nWAIT pin has been asserted, it will begin inserting extra strobe
cycles into the operation until the EMIF_nWAIT pin is deactivated by the external device. The EMIF will
then return to the last cycle of the programmed strobe period and the operation will proceed as usual from
this point. Please refer to the device data manual for details on the timing requirements of the
EMIF_nWAIT signal.
The EMIF_nWAIT pin cannot be used to extend the strobe period indefinitely. The programmable
MAX_EXT_WAIT field in the asynchronous wait cycle configuration register (AWCC) determines the
maximum number of EMIF_CLK cycles the strobe period may be extended beyond the programmed
length. When the counter expires, the EMIF proceeds to the hold period of the operation regardless of the
state of the EMIF_nWAIT pin. The EMIF can also generate an interrupt upon expiration of this counter.
See
for details on enabling this interrupt.
For the EMIF to function properly in the Extended Wait mode, the WP
n
bit of AWCC must be programmed
to match the polarity of the EMIF_nWAIT pin. In its reset state of 1, the EMIF will insert wait cycles when
the EMIF_nWAIT pin is sampled high. When set to 0, the EMIF will insert wait cycles only when
EMIF_nWAIT is sampled low. This programmability allows for a glueless connection to larger variety of
asynchronous devices.
Finally, a restriction is placed on the strobe period timing parameters when operating in Extended Wait
mode. Specifically, the sum of the W_SETUP and W_STROBE fields must be greater than 4, and the sum
of the R_SETUP and R_STROBE fields must be greater than 4 for the EMIF to recognize the
EMIF_nWAIT pin has been asserted. The W_SETUP, W_STROBE, R_SETUP, and R_STROBE fields are
in CE
n
CFG.