memory products - Al Kossow's Bitsavers

MK41H80(N,P)-20/25/35APPLICATIONThe MK41H80 operates from a 5.0 volt supply. It iscompatible with all standard TTL families on all inputsand outputs. The device should share a solidground plane with any other devices interfaced withit, particularly TTL devices. Additionally, becausethe outputs can drive rail-to-rail into high impedanceloads, the MK41H80 can also interface to 5 voltCMOS on all inputs and outputs. Refer to the normalizedperformance curves that follow.The MK41H80 compares contents of addressedRAM locations to the current data inputs. A logicone (1) output on the MATCH pin indicates that theinput data and the RAM contents match. Conversely,a logic zero (0) on the MATCH pin indicates atleast one bit difference between the RAM contentsand input data generating a miss.The MATCH output is always at either an active highor low logic level, and does not exhibit a threestateor high impedance characteristic. Since thecomparator circuitry is always enabled, metastabledata input levels can result in excessive MATCH output activity. Therefore, the use of pull-up or pulldownresistors is recommended on the data bus.A pull-up resistor is also recommended for the CLRinput. This will ensure that any low going systemnoise, coupled onto the input, does not drive CLRbelow V 1H minimum specifications.Because high frequency current transients will beassociated with the operation of the MK41H80, powerlines inductance must be minimized on the circuitboard power distribution network. Power andground trace gridding or separate power planes canbe employed to reduce line inductance.Though often times not thought of as such, thetraces on a memory board are basically unterminated,low impedance transmission lines. As suchthey are subject to signal reflections manifested asnoise, undershoots and excessive ringing. Seriestermination in close proximity to the TTL drivers canimprove driver/signal path impedance matching.While experimentation most often proves to be theonly practical approach to selection of series resistors,values in the range of 10 to 33 ohms oftenprove most suitable.FIGURE 4. BLOCK DIAGRAM141I Ao~~~SS I I ROW IDECODERl BUFFER JICLEARBUFFERI l WRITE WRITEENABLE II BUFFERCONTROLDATA INPUTBUFFERI4 1MEMORYCELL ARRAY128 ROWS32x4 COWMNS44 4·BITCOLUMN 4 COMPARATORI/OMATCH5-I ;~D~:'SNS II BUFFER I5 COLUMNDECODER·1OUTPUTENABLEBUFFER4~DATAOUTPUTBUFFER44110358