at40k20al-1dqc ATMEL Corporation, at40k20al-1dqc Datasheet - Page 12

• Manufacturer Part Number: at40k20al-1dqc
• Description: At40k05al 5k - 50k Gates Coprocessor Fpga With Freeram
• Manufacturer: ATMEL Corporation

12
AT40KAL Series FPGA
Reading and writing of the 10 ns 32 x 4 dual-port FreeRAM are independent of each
other. Reading the 32 x 4 dual-port RAM is completely asynchronous. Latches are
transparent; when Load is logic 1, data flows through; when Load is logic 0, data is
latched. These latches are used to synchronize Write Address, Write Enable Not, and
Din signals for a synchronous RAM. Each bit in the 32 x 4 dual-port RAM is also a trans-
parent latch. The front-end latch and the memory latch together form an edge-triggered
flip flop. When a nibble (bit = 7) is (Write) addressed and LOAD is logic 1 and WE is
logic 0, data flows through the bit. When a nibble is not (Write) addressed or LOAD is
logic 0 or WE is logic 1, data is latched in the nibble. The two CLOCK muxes are con-
trolled together; they both select CLOCK (for a synchronous RAM) or they both select
“1” (for an asynchronous RAM). CLOCK is obtained from the clock for the sector-column
immediately to the left and immediately above the RAM block. Writing any value to the
RAM clear byte during configuration clears the RAM (see the “AT40K/40KAL Configura-
tion Series” application note at www.atmel.com).
Figure 8. RAM Logic
Figure 9 on page 13 shows an example of a RAM macro constructed using the
AT40KAL’s FreeRAM cells. The macro shown is a 128 x 8 dual-ported asynchronous
RAM. Note the very small amount of external logic required to complete the address
decoding for the macro. Most of the logic cells (core cells) in the sectors occupied by the
RAM will be unused: they can be used for other logic in the design. This logic can be
automatically generated using the macro generators.
WEN
Aout
Ain
Din
5
5
4
“1”
0
1
Latch
Latch
Latch
Load
Load
Load
CLOCK
Read Address
Write Address
Write Enable NOT
Din
RAM-Clear Byte
Dual-port
Clear
1
Load
32 x 4
RAM
“1”
0
Dout
“1”
OE
2818F–FPGA–07/06
4
Dout