TA
w
ǒ
t
EM_CS
)
t
COD
(m)
)
t
EM_D
Ǔ
t
cyc
*
1
R_HOLD
w
ǒ
t
H
*
t
EM_D
*
t
OH
(m)
*
t
EM_A
Ǔ
t
cyc
*
1
R_SETUP
)
R_STROBE
)
R_HOLD
w
t
RC
(m)
t
cyc
*
3
R R_STROBE
≥
t
EM_A
t
ACC
(m)
t
SU
t
EM_D
t
cyc
- 2
(
)
+
+
+
Example Configuration
884
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface A (EMIFA)
19.3.2.2.2 Taking Into Account PCB Delays
The equations described in
are for the ideal case, when board design does not
contribute delays. Board characteristics, such as impedance, loading, length, number of nodes, etc., affect
how the device driver behaves. Signals driven by the EMIFA will be delayed when they reach the ASRAM
and conversely.
lists the delays shown in
and
due to PCB affects.
The PCB delays are board specific and must be estimated or determined though the use of IBIS modeling.
The signals denoted (ASRAM) are the signals seen at the ASRAM. For example, EMA_CS represents the
signal at the EMIFA and EMA_CS (ASRAM) represents the delayed signal seen at the ASRAM.
Table 19-35. ASRAM Timing Requirements With PCB Delays
Parameter
Description
Read Access
t
EM_CS
Delay on EMA_CS from EMIFA to ASRAM. EMA_CS is driven by EMIF.
t
EM_A
Delay on EMA_A from EMIFA to ASRAM. EMA_A is driven by EMIF.
t
EM_OE
Delay on EMA_OE from EMIFA to ASRAM. EMA_OE is driven by EMIF.
t
EM_D
Delay on EMA_D from ASRAM to EMIFA. EMA_D is driven by ASRAM.
Write Access
t
EM_CS
Delay on EMA_CS from EMIFA to ASRAM. EMA_CS is driven by EMIF.
t
EM_A
Delay on EMA_A from EMIFA to ASRAM. EMA_A is driven by EMIF.
t
EM_WE
Delay on EMA_WE from EMIFA to ASRAM. EMA_WE is driven by EMIF.
t
EM_D
Delay on EMA_D from EMIFA to ASRAM. EMA_D is driven by EMIF.
From
, the following equations may be derived. t
cyc
is the period at which the EMIFA operates.
The R_SETUP, R_STROBE, and R_HOLD fields are programmed in terms of EMIFA cycles where as the
data sheet specifications are typically given in nano seconds. This is explains the presence of t
cyc
in the
denominator of the following equations. A minus 1 is included in the equations because each field in
CE
n
CFG is programmed in terms of EMIFA clock cycles, minus 1 cycle. For example, R_SETUP is equal
to R_SETUP width in EMIFA clock cycles minus 1 cycle.