memory products - Al Kossow's Bitsavers

MK45264/45265(N)-55noReadlWriteThe FIFOs utilize separate Read and Write enableinputs to control port activity and direction. A lowon a Read Enable reads a port's receive FIFO. Ahigh on a Read Enable or a low on a Write Enabledisables a port's data outputs to a high impedancestate. A low on a Write Enable initiates a write toa port's transmit FIFO, regardless of the state ofRead Enable. Input data is latched into the FIFOon the rising edge of a Write Enable.Full/Empty FlagsAn active Full Flag indicates that a port's transmitFIFO is full and will accept no more data. Writesdone to a FIFO while full are blocked. Once a readhas occurred on a full FIFO, clearing a location inthe FIFO, the Full Flag will go inactive, allowinganother write to begin on the next falling edge ofWrite Enable.An active Empty Flag indicates a port's receive FIFOis empty and can send no more data. Any readsdone on a FIFO while empty are blocked. Once awrite to an empty FIFO has occurred, the EmptyFlag will go inactive, allowing another read to beginon the next falling edge of Read Enable.FIGURE 4. WRITE TIMINGAlmost FlagsAn inactive Almost Full flag indicates a port's transmitFIFO has room for at least four (4) more bytes,which is to say the flag will go active during thefourth write from full and stay active until after thefourth location from full has been vacated (read).An inactive Almost Empty flag indicates a port'sreceive FIFO has at least four (4) bytes of data inmemory, ready to be read, which is to say that theflag will go active while reading the fourth remainingbyte and remain active until after the fourth bytehas been stored (written).ResetReset is initiated by a low on the Master Reset (RS)input. A reset returns all data outputs to a high impedance..,§!ate, takin9...Preced~nce over the readstrobes (Rx/DIR andfu) and§.:. The states of theFIFO control inputs (Rx/DIR, Wx, Ry and Wy) area Don't Care throughout reset. The read strobes area Don't Care at the end of reset because the EmptyFlag becomes active (goes low) during reset,blocking ~ attempted reads. The write strobes(Wx and Wy) may fall any time during....Q!. afterreset, but must not go high until t RSR after RS goeshigh.tet. tAt.WxtOHtOHDOxDATA INDATA IN6118462