Same-Port Read-During-Write Mode; Mixed-Port Read-During-Write Mode - Altera Cyclone IV Device Handbook

3–16

Same-Port Read-During-Write Mode

This mode applies to a single-port RAM or the same port of a true dual-port RAM. In
the same port read-during-write mode, there are two output choices: New Data mode
(or flow-through) and Old Data mode. In New Data mode, 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.
When using New Data mode together with byteena, you can control the output of the
RAM. When byteena is high, the data written into the memory passes to the output
(flow-through). When byteena is low, the masked-off data is not written into the
memory and the old data in the memory appears on the outputs. Therefore, the
output can be a combination of new and old data determined by byteena.
Figure 3–14
read-during-write behavior with both New Data and Old Data modes, respectively.
Figure 3–14. Same Port Read-During Write: New Data Mode
Figure 3–15. Same Port Read-During-Write: Old Data Mode

Mixed-Port Read-During-Write Mode

This mode applies to a RAM in simple or true dual-port mode, which has one port
reading and the other port writing to the same address location with the same clock.
Cyclone IV Device Handbook,
Volume 1
and Figure 3–15 show sample functional waveforms of same port
clk_a
wren_a
rden_a
address_a
data_a
A
q_a (asynch)
A
clk_a
wren_a
rden_a
address_a
data_a
A
q_a (asynch)
a0(old data)
Chapter 3: Memory Blocks in Cyclone IV Devices
a0
B C D
B C D
a0
B C D
A B
a1(old data)
Design Considerations
a1
E F
E
F
a1
E F
D E
November 2011 Altera Corporation