EP2AGX95EF29C6N Datasheet, PDF (69/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 3: Memory Blocks in Arria II Devices
Design Considerations
3–21
Read-During-Write Behavior
You can customize the read-during-write behavior of the Arria II memory blocks to
suit your design requirements. The two types of read-during-write operations are
same port and mixed port. Figure 3–19 shows the difference between the same port
and mixed port.
Figure 3–19. Read-During-Write Data Flow
Port A
data in
Port A
data out
Port B
data in
Port B
data out
Mixed-port
data flow
Same-port
data flow
Same-Port Read-During-Write Mode
This mode applies to either a single-port RAM or the same port of a true dual-port
RAM. In same-port read-during-write mode, three output choices are available: new
data mode (or flow-through), old data mode, or don’t care mode. In new data mode,
the new data is available on the rising edge of the same clock cycle on which it was
written. In old data mode, the RAM outputs reflect the old data at that address before
the write operation proceeds. In don’t care mode, the RAM outputs “don’t care”
values for a read-during-write operation.
Figure 3–20 shows sample functional waveforms of same-port read-during-write
behavior in don’t care mode for MLABs.
Figure 3–20. MLABs Blocks Same Port Read-During Write: Don’t Care Mode
clk_a
address XX
A0
data_in _XX
wrena
FFFF
q(unregistered) XX A0(old data)
q(registered)
XX
FFFF
A1(old data)
FFFF
A1
AAAA
A2
XXXX
AAAA
A2(old data)
AAAA
December 2011 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration