HM-6551 Intersil Corporation, HM-6551 Datasheet - Page 7

• Manufacturer Part Number: HM-6551
• Description: 256 X 4 Cmos Ram
• Manufacturer: Intersil Corporation

Timing Waveforms
In the Write Cycle the falling edge of E latches the addresses
and S2 into on-chip registers. S2 must be latched in the low
state to enable the device. The write portion of the cycle is
defined as E, W, S1 being low and S2 being latched simulta-
neously. The W line may go low at any time during the cycle
providing that the write pulse setup times (TWLEH and
TWLS1H) are met. The write portion of the cycle is terminated
on the first rising edge of either E, W, or S1.
If a series of consecutive write cycles are to be executed, the
W line may be held low until all desired locations have been
written. If this method is used, data setup and hold times must
be referenced to the first rising edge of E or S1. By positioning
REFERENCE
TIME
REFERENCE
-1
0
1
2
3
4
5
TIME
S2
S1
W
A
E
D
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E
H
H
L
L
(Continued)
(9) TS2LEL
(8) TAVEL
S1
H
H
X
X
X
TEHEL (7)
L
L
-1
S2
X
X
X
X
X
L
L
INPUTS
0
TELS2X
VALID
TELAX
(11)
(10)
FIGURE 2. WRITE CYCLE
W
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H
X
X
X
X
HM-6551/883
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1
TRUTH TABLE
6-107
A
X
V
X
X
X
X
V
TELWH (17)
TS1LWH (16)
the write pulse at different times within the E and S1 low time
(TELEH), various types of write cycles may be performed. If
the S1 low time (TS1LS1H) is greater than the W pulse, plus
an output enable time (TS1LQX), a combination read-write
cycle is executed. Data may be modified an indefinite number
of times during any write cycle (TELEH).
The HM-6551/883 may be used on a common I/O bus struc-
ture by tying the input and output pins together. The multiplex-
ing is accomplished internally by the W line. In the write cycle,
when W goes low, the output buffers are forced to a high
impedance state. One output disable time delay (TWLQZ)
must be allowed before applying input data to the bus.
TELEH (6)
TWLWH (18)
TWLEH (15)
TDVWH (12)
DATA VALID
TWLS1H (14)
D
X
X
X
V
X
X
X
TELEL (19)
OUTPUTS
Q
Z
Z
Z
Z
Z
Z
Z
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2
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3
Memory Disabled
Cycle Begins, Addresses and S2 are
Latched
Write Period Begins
Data In is Written
Write is Completed
Prepare for Next Cycle (Same as -1)
Cycle Ends, Next Cycle Begins
(Same as 0)
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TWHDX (13)
(8) TAVEL
(9) TS2LEL
TEHEL (7)
FUNCTION
4
5
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