Architecture
849
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface A (EMIFA)
19.2.4.11 Mapping from Logical Address to EMIFA Pins
When the EMIFA receives an SDRAM access request, it must convert the address of the access into the
appropriate signals to send to the SDRAM device. The details of this address mapping are shown in
for 16-bit operation. Using the settings of the IBANK and PAGESIZE fields of the SDRAM
configuration register (SDCR), the EMIFA determines which bits of the logical address are mapped to the
SDRAM row, column, and bank addresses.
As the logical address is incremented by one halfword (16-bit operation), the column address is likewise
incremented by one until a page boundary is reached. When the logical address increments across a
page boundary, the EMIFA moves into the same page in the next bank of the attached device by
incrementing the bank address EMA_BA and resetting the column address. The page in the previous
bank is left open until it is necessary to close it. This method of traversal through the SDRAM banks helps
maximize the number of open banks inside of the SDRAM and results in an efficient use of the device.
There is no limitation on the number of banks that can be open at one time, but only one page within a
bank can be open at a time.
The EMIFA uses the EMA_WE_DQM pins during a WRT command to mask out selected bytes or entire
words. The EMA_WE_DQM pins are always low during a READ command.
Table 19-13. Mapping from Logical Address to EMIFA Pins for 16-bit SDRAM
IBANK
PAGESIZE
Logical Address
31:27
26
25
24
23
22
21:14
13
12
11
10
9
8:1
0
0
0
-
Row Address
Col Address
EMA_WE_DQM[0]
1
0
-
Row Address
EMA_BA[0]
Col Address
EMA_WE_DQM[0]
2
0
-
Row Address
EMA_BA[1:0]
Col Address
EMA_WE_DQM[0]
0
1
-
Row Address
Column Address
EMA_WE_DQM[0]
1
1
-
Row Address
EMA_BA[0]
Column Address
EMA_WE_DQM[0]
2
1
-
Row Address
EMA_BA[1:0]
Column Address
EMA_WE_DQM[0]
0
2
-
Row Address
Column Address
EMA_WE_DQM[0]
1
2
-
Row Address
EMA_BA[0]
Column Address
EMA_WE_DQM[0]
2
2
-
Row Address
EMA_BA[1:0]
Column Address
EMA_WE_DQM[0]
0
3
-
Row Address
Column Address
EMA_WE_DQM[0]
1
3
-
Row Address
EMA_BA[0]
Column Address
EMA_WE_DQM[0]
2
3
-
Row Address
EMA_BA[1:0]
Column Address
EMA_WE_DQM[0]
NOTE:
The upper bit of the Row Address is used only when addressing 256-Mbit and 512-Mbit
SDRAM memories.