SRAM is one of random access memories. Each byte or word has an address and can be accessed randomly. SRAM
has three different modes supported. Each function is described below with Truth Table. Below description is based on
the device with 2 CS pins.
Device enters standby mode when deselected (CS1# HIGH or CS2 LOW or both UB# and LB# are HIGH). The input
and output pins (I/O0-15) are placed in a high impedance state. The current consumption in this mode will be ISB1 or
ISB2. CMOS input in this mode will maximize saving power.
Write operation issues with Chip selected (CS1# LOW and CS2 HIGH) and Write Enable (WE#) input LOW. The input
and output pins (I/O0-15) are in data input mode. Output buffers are closed during this time even if OE# is LOW. UB#
and LB# enables a byte write feature. By enabling LB# LOW, data from I/O pins (I/O0 through I/O7) are written into the
location specified on the address pins. And with UB# being LOW, data from I/O pins (I/O8 through I/O15) are written
into the location.
Read operation issues with Chip selected (CS1# LOW and CS2 HIGH) and Write Enable (WE#) input HIGH. When
OE# is LOW, output buffer turns on to make data output. Any input to I/O pins during READ mode is not permitted. UB#
and LB# enables a byte read feature. By enabling LB# LOW, data from memory appears on I/O0-7. And with UB#
being LOW, data from memory appears on I/O8-15.
In the READ mode, output buffers can be turned off by pulling OE# HIGH. In this mode, internal device operates as
READ but I/Os are in a high impedance state. Since device is in READ mode, active current is used.