
SEC ASIC
5-49
STD80/STDM80
DPSRAM Gen
Dual-Port Synchronous RAM Generator
Pin Descriptions
Name
CK1
CK2
CSN1
CSN2
Pin Capacitance
CK
(Unit = SL)
Application Notes
1)
As you will see in the timing diagrams, DOUT1 [ ] (DOUT2 [ ]) is valid only when CK1 (CK2) is high. If you
want DOUT1 [ ] (DOUT2 [ ]) to be stable regardless of CK1 (CK2) state, you should put STD80/STDM80
Busholder cells on the DOUT1 [ ] (DOUT2 [ ]) bus externally.
Putting Busholders on DOUT1 [ ] and DOUT2 [ ]
2)
Aspect ratio is programmable using low address decoder types. As you can see in the configuration table,
there are up to 5 selections of Ymux for the same Words and the same Bpw DPSRAM. You can choose one
of them in accordance with your chip level layout preference. Larger Ymux means fatter and shorter aspect
ratio and smaller Ymux means thinner and taller aspect ratio. As you can see in the characteristic tables,
aspect ratio affects major characteristics of DPSRAM, In general, larger Ymux DPSRAM has faster speed
and bigger area than smaller Ymux DPSRAM.
Customizing Aspect Ratio
3)
Simultaneous accesses to the same location through both ports cause a contention. DPSRAM has no
contention preventing scheme. You have to take care of the contention modes. Please refer to the timing
diagrams of contention modes to get more information of contention modes.
Contention Modes
I/O
I
Description
“Clock”s serve as input clocks to each port of the memory block. When CK1 (CK2) is
low, port1 (port2) is in a precharge state. Upon the rising edge, an access begins.
“Chip Select Negative”s act as each port’s enable signal for selections of multiple
blocks on a common clock. When CSN1 (CSN2) is high, port1 (port2) goes to
stand-by (power down) mode and no access can occur, conversely, if low only then
may a read or write access occur. CSN1 (CSN2) may not change during CK1 (CK2)
is high.
“Write Enable Negative”s select the type of memory access. Read is the high state,
and write is the low state.
I
WEN1
WEN2
OEN1
OEN2
A1 [ ]
A2 [ ]
DI1 [ ]
DI2 [ ]
DOUT1 [ ]
DOUT2 [ ]
I
I
“Output Enable Negative”s control the output drivers from driven to tri-state condi-
tion. OEN1 (OEN2) may not change during CK1 (CK2) is high.
I
“Address”es select the location to be accessed. A1 [ ] (A2 [ ]) may not change during
CK1 (CK2) is high.
I
When CK1 (CK2) rises while WEN1 (WEN2) is low, the “Data In” word value is
written to the accessed location.
During a read access, data word stored will be presented to the “Data Out” ports.
DOUT1 [ ] and DOUT2 [ ] are tri-statable. Only when CK1 (CK2) is high, CSN1
(CSN2) and OEN1 (OEN2) is low, DOUT1 [ ] (DOUT2 [ ]) drives a certain value.
Otherwise, DOUT1 [ ] (DOUT2 [ ]) keeps Hi-Z state. During a write access, data
word written will be presented at the “Data Out” ports if output driver is enabled.
O
CSN
WEN
OEN
A
DI
DOUT
Ymux 8
12.0
Ymux 2
5.4
Ymux 4
5.4
Ymux 16 Ymux 32
25.0
5.8
1.9
0.9
2.3
1.0
2.0
51.0