74F524 Datasheet, PDF (3/14 Pages) NXP Semiconductors – 8-bit register comparator open-collector 3-State

Philips Semiconductors
8-bit register comparator (open collector + 3-State)
Product specification
74F524
LOGIC SYMBOL for 74F456
12
18
M
17
C/SI
1
S0
19
S1
11
CP
SE
C/SO
16
LT
13
GT
14
EQ
15
I/O0 I/O1 I/O2 I/O3 I/O4 I/O5 I/O6 I/O7
2 3456789
V_CC = Pin 20
GND = Pin 10
SF00971
LOGIC SYMBOL (IEEE/IEC) for 74F456
COMP
1
0=HOLD
19
0
1
M
0
3
1=READ
2=SHIFT
11
C4/2/4
3=LOAD
12
M5 MAGNITUDE
2D
16
M6 TWO’s COMPLEMENT
17
&
18
G7
2
3, 4D
13
1,5,6,7>I/O
3
1,5,6,7<I/O
14
4
1,5,6,7=I/O
15
5
6
7
8
9
SF00972
FUNCTIONAL DESCRIPTION
The 74F524 contains eight D-type flip-flops connected as a shift
register with provision for either parallel or serial loading. Parallel
data may be read from or loaded into the registers via the data bus
I/O0–I/O7. Serial data is loaded into the register from the C/SI input
and may be shifted through the register and out through the C/SO
output. Both parallel and serial data entry occurs on the rising edge
of the clock (CP). The operation of the shift register is controlled by
two signals, S0 and S1, according to the Select Function Table. The
3-State parallel output buffers are enabled only in the READ mode.
SELECT FUNCTION TABLE
S0
S1
OPERATION
L
L HOLD–Retains data in shift register
L
H READ–Read contents in register onto data bus
H
L SHIFT–Allows serial shifting on next rising clock
edge
H
H LOAD–Load data on bus into register
H = High voltage level
L = Low voltage level
One port of an 8-bit comparator is attached to the data bus while the
other port is tied to the outputs of the internal register. Three
active-OFF Open Collector outputs indicate whether the contents
held in the shift register are ‘greater than’ (GT). ‘less than’ (LT), or
‘equal to’ (EQ) the data on the input bus. A High signal on the Status
Enable (SE) input disables these outputs to the OFF state. A mode
control (M) input allows selection between a straightforward
magnitude compare or a comparison between Two’s complement
numbers.
NUMBER REPRESENTATION SELECT TABLE
M
OPERATION
L Magnitude compare
H Two’s Complement compare
H = High voltage level
L = Low voltage level
For ‘greater than’ or ‘less than’ detection, the C/SI input must be
held High, as indicated in the Function Table. The internal logic is
arranged such that a Low signal on the C/SI input places the
‘greater than’ and ‘less than’ outputs in their off state. (Note that this
off state serves also as the active state when C/SI is High. It is
intended for use in expansion to word lengths greater than 8 bits
using multiple 74S524s as explained in the next 3 paragraphs.) The
C/SO output will be forced High if the ‘equal to’ status condition
exists; otherwise, C/SO will be held Low.
Word length expansion (in groups of 8 bits) can be achieved by
connecting the C/SO output of the more significant byte to the C/SI
input of the next less significant byte and also to its own SE input
(see Application Figure 1). The CS/I input of the most significant
device is held High while the SE input of the least significant device
is held Low. The corresponding status outputs are AND-wired
together. In the case of two’s complement number compare, only the
Mode input to the most significant device should be High. the Mode
inputs to all other cascaded devices are held Low.
Suppose that an inequality condition is detected in the most
significant device. Assuming that the byte stored in the register is
greater than the byte on the data bus, then the EQ and LT outputs
will be pulled Low, whereas the GT output will float High. Also, the
1990 Aug 07
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