memory products - Al Kossow's Bitsavers

TS27C256QDEVICE OPERATIONThe seven modes of operation of the TS27C256are listed in the Operating Modes table. A single5V power supply is required in the read mode. Allinputs are TTL levels except for Vpp.READ MODEThe TS27C256 has two control functions, both ofwich must be logically active in order to obtain dataat the outputs. Chip Enable (CE) is the powercontrol and should be used for device selection.Output Enable (OE) is the output control and shouldbe used to gate data to the output pins, independentof device selection. Assuming that addressesare stable, address access time (tACC) is equal tothe delay from CE to Output (tCe). Data is availableat the oUJrults after a delay of tOE from the fallingedge of OE, assuming that CE has been low andaddresses have been stable for at leasttAcc-tOE.STANDBY MODEThe TS27C256 has a standby mode which reducesthe maximum power dissipation to 5.5 mW. TheTS27C256 is placed in the standby mode by applyinga TTL high signal to the CE input. When instandby mode, the outputs are in a high impedancestate, independent of the OE input.OUTPUT OR-TYINGBecause EPROMs are usually used in larger memoryarrays, we have provided two control lineswhich accomodate this multiple memory connection.The two control lines allow for:a) the lowest possible memory power dissipation,andb) complete assurance that output bus contentionwill not occur.To use these control lines most efficiently, CE (pin20) should be decoded and used as the primary deviceselecting function, while OE (pin 22) should bemade a common connection to all devices in thearray and connected to the READ line from the systemcontrol bus. This assures that all deselectedmemory devices are in their low power standby modesand that the output pins are active only whendata is desired from a particular memory device.PROGRAMMING MODESCaution: Exceeding 14Von pin 1 (VppJ will damagethe TS27C256.Initially, . and after each erasure, all bits of theTS27C256 are in the "1" state. Data is introducedby selectively programming "Os" into the desiredbit locations. Although only "Os" will be programmed,both "1s" and "Os" can be presented in thedata word. The only way to change a "0" to a "1"is by ultraviolet light erasure.The TS27C256 is in the programming mode whenthe Vpp input is at 12.5 V and CE is at TTL Low.It is required that a 0.1 I'F capaCitor be placedacross Vpp, VCC and ground to suppress spuriousvoltage transients which may damage the device.The data to be programmed is applied 8 bits in parallelto the data output pins. The levels requiredfor the address and data inputs are TTL.Programming of multiple TS27C256s in parallelwith the same data can be easily accomplished dueto the simplicity of the programming requirements.Like inputs of the parallel TS27C256s may be connectedtogether when they are programmed withthe same data. A low level TTL pulse applied tothe CE input programs the paralleled TS27C256s.HIGH SPEED PROGAMMINGThe high speed programming algorithm describedin the flow chart rapidly programs TS27C256 usingan efficient and reliable method particularly suitedto the production programming environment. Typicalprogramming times for individual devices areon the order of 5 minutes.PROGRAM INHIBITProgramming of multiple TS27C256s in parallelwith different data is also easily accomplishedMusing the program inhibit mode. A high level on CEinput inhibits the other TS27C256S from being pro-9@mmed. Except for CE, all like inputs (includingOE) of the parallel TS27C256s may be common.A TTL low-level pulse applied to a TS27C256 CEinput with Vpp at 12.5 V will program thatTS27C256.PROGRAM VERIFYA verify may be performed on the programmed bitsto determine that they were correctly proQ@mmed.The verify is performed with OE at VIL, CE at VIHand Vpp at 12.5 V.ELECTRONIC SIGNATURE MODEElectronic signature mode allows the reading outof a binary code that will indentify the EPROM manufacturerand type. This mode is intended for useby programming equipment for the purpose of automaticallymatching the device to be programmedwith its corresponding programming algorithm. Thismode is functional in the 25°C ±5°C ambient temperaturerange that is required when programmingthe TS27C256. To activate this mode the programmingequipment must force 11.5V to 12.5V on addressline A9 (pin 24) of the TS27C256. Two bytesmay then be sequenced from the device outputsby toggling address line AD (pin 10) from VIL toVIH. All other address lines must be held at VIL duringelectonic signature mode.5/9125