
STD80/STDM80
5-4
SEC ASIC
CROM Gen
Contact Programmable Synchronous ROM Generator
Pin Descriptions
Name
CK
Pin Capacitance
(Unit = SL)
Application Notes
1)
As you will see in the timing diagrams, DOUT [ ] is valid only when CK is high. If you want DOUT [ ] to be
stable regardless of CK state, you should put STD80/STDM80 Busholder cells on the DOUT [ ] bus
externally.
Putting Busholders on DOUT [ ]
2)
Aspect ratio is programmable using low address decoder types. As you can see in the configuration table,
there are up to 4 selections of Ymux for the same Words and the same Bpw CROM. 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 CROM, In general, larger Ymux CROM has faster speed and
bigger area than smaller Ymux CROM.
Customizing Aspect Ratio
3)
To enlarge the capacity of CROM, we added one more option to choose number of banks. If you want to use
larger CROM than 64K bit CROM, you can select dual bank (ba = 2). You can also select dual bank for
smaller one than 64K bit CROM. Dual bank CROM is a little bigger and a little faster than single bank one.
(Please refer to the characteristic tables.)
Selecting Number of Banks
I/O
I
Description
“Clock” serves as the input clock to the memory block. When CK is low the memory
is in a precharge state. Upon the rising edge, an access cycle begins.
“Chip Select Negative” acts as the memory enable signal for selections of multiple
blocks on a common clock. When CSN is high, the memory goes to stand-by (power
down) mode and no access to the memory can occur, conversely, if low only then
may a read access occur. CSN may not change during CK is high.
“Output Enable Negative” controls the output drivers from driven to tri-state
condition. OEN may not change during CK is high.
“Address” selects the location to be accessed. A [ ] may not change during CK is
high.
During a read access, data word programmed will be presented to the “Data Out”
ports. DOUT [ ] is tri-statable. When CK is high, CSN is low and OEN is low, only
then, DOUT [ ] drives a certain value. Otherwise, DOUT [ ] keeps Hi-Z state.
CSN
I
OEN
I
A [ ]
I
DOUT [ ]
O
CK
CSN
OEN
A
DOUT
Ymux 4
4.0
4.0
Ymux 8
8.7
8.7
Ymux 16
18.0
18.0
Ymux 32
37.0
37.0
1-bank
2-bank
5.8
11.5
1.8
3.7
2.2
4.4
1.7
1.7