74LS670/54LS670 pdf datasheet

54LS670/DM54LS670/DM74LS670
TRI-STATEÉ 4-by-4 Register Files
General Description
These register files are organized as 4 words of 4 bits each,
and separate on-chip decoding is provided for addressing
the four word locations to either write-in or retrieve data.
This permits writing into one location, and reading from another
word location, simultaneously.
Four data inputs are available to supply the word to be
stored. Location of the word is determined by the write select
inputs A and B, in conjunction with a write-enable signal.
Data applied at the inputs should be in its true form.
That is, if a high level signal is desired from the output, a
high level is applied at the data input for that particular bit
location. The latch inputs are arranged so that new data will
be accepted only if both internal address gate inputs are
high. When this condition exists, data at the D input is transferred
to the latch output. When the write-enable input, GW,
is high, the data inputs are inhibited and their levels can
cause no change in the information stored in the internal
latches. When the read-enable input, GR, is high, the data
outputs are inhibited and go into the high impedance state.
The individual address lines permit direct acquisition of data
stored in any four of the latches. Four individual decoding
gates are used to complete the address for reading a word.
When the read address is made in conjunction with the
read-enable signal, the word appears at the four outputs.
This arrangementÐdata entry addressing separate from
data read addressing and individual sense line Ð eliminates
recovery times, permits simultaneous reading and writing,
and is limited in speed only by the write time (27 ns typical)
and the read time (24 ns typical). The register file has a nonvolatile
readout in that data is not lost when addressed.
All inputs (except read enable and write enable) are buffered
to lower the drive requirements to one normal Series
54LS/74LS load, and input clamping diodes minimize
switching transients to simplify system design. High speed,
double ended AND-OR-INVERT gates are employed for the
read-address function and have high sink current, TRISTATE
outputs. Up to 128 of these outputs may be wire-
AND connected for increasing the capacity up to 512 words.
Any number of these registers may be paralleled to provide
n-bit word length.