SDRAM Mode
1233
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
External Peripheral Interface (EPI)
17.6.1 External Signal Connections
defines how EPI module signals should be connected to SDRAMs. The table applies when
using a x16 SDRAM up to 512 megabits. Any unused EPI controller signals can be used as GPIOs or
another alternate function.
(1)
If 2 signals are listed, connect the EPI signal to both pins.
(2)
Only for 256/512 megabit SDRAMs.
Table 17-1. EPI SDRAM Signal Connections
EPI Signal
SDRAM Signal
(1)
EPI0S0
A0
D0
EPI0S1
A1
D1
EPI0S2
A2
D2
EPI0S3
A3
D3
EPI0S4
A4
D4
EPI0S5
A5
D5
EPI0S6
A6
D6
EPI0S7
A7
D7
EPI0S8
A8
D8
EPI0S9
A9
D9
EPI0S10
A10
D10
EPI0S11
A11
D11
EPI0S12
A12
(2)
D12
EPI0S13
BA0
D13
EPI0S14
BA1
D14
EPI0S15
D15
EPI0S16
DQML
EPI0S17
DQMH
EPI0S18
CAS
EPI0S19
RAS
EPI0S20-EPI0S27
not used
EPI0S28
WE
EPI0S29
CS
EPI0S30
CKE
EPI0S31
CLK
17.6.2 Refresh Configuration
The refresh count is based on the external clock speed and the number of rows per bank as well as the
refresh period. The RFSH field represents how many external clock cycles remain before an AUTO-
REFRESH is required. The normal formula is:
RFSH = (t
Refresh_µs
/ number_rows) /ext_clock_period
A refresh period is normally 64 ms, or 64000 µs. The number of rows is normally 4096 or 8192.The
ext_clock_period is a value expressed in µsand is derived by dividing 1000 by the clock speed expressed
in MHz. So, 50 MHz is 1000/50=20 ns, or 0.02 µs. A typical SDRAM is 4096 rows per bank if the system
clock is running at 50 MHz with an EPIBAUD register value of 0:
RFSH = (64000/4096) / 0.02 = 15.625 µs /0.02 µs = 781.25