memory products - Al Kossow's Bitsavers

ST27256PDEVICE OPERATION (Continued)PROGRAM INHIBITProgramming of multiple ST27256Ps in parallel withdifferent data is also easily acco..mplished. Exceptfor CE, all like inputs (including OE) of the parallelST27256P may be common. A TTL low pulse appliedto a ST27256P's CE input, with Vpp at 12.5V,will program that ST27256P. A high level CE inputinhibits the other ST27256Ps from being programmed.PROGRAM VERIFYA verify should be performed on the programmedbits to determine that they were correctlypro9.@!!1med. The verify is accomplished with OE atV1L, CE at V1H and Vpp at 12.5V.OPTIONAL VERihThe optional verify may be performed instead....Q!the verify mode. It is performed with OE at V1L, CEat V1L (as opposed to the standard verify which hasCE at V1H), and Vpp at 12.5V. The outputs willthree-state according to the signal presented to OE.Therefore, all devices with Vpp = 12.5V andOE = 'liLwili present data on the bus independentof the CE state. When parallel programming severaldevices which share the common bus, Vpp shouldbe lowered to Vee (= 6V) and the normal readmode used to execute a program verify.ELECTRONIC SIGNATUREThe Electronic Signature mode allows the readingout of a binary code from an EPROM that will identifyits manufacturer and type. This mode is intendedfor use by programming equipment for the purposeof automatically matching the device to beprogrammed with its corresponding programmingalgorithm. This mode is functional in. the 25°C±5°C ambient temperature range that is requiredwhen programming the ST27256P. To activate thismode, the programming equipment must force11.5V to 12.5V on address line A9' (pin 24) of theST27256P.Two identifier bytes may then be sequenced fromthe device outputs by toggling address line AD (pin10) from V1L to V1H. All other address lines must beheld at V1L during Electronic Signature mode. Byteo (AO = V1J represents the manufacturer code andbyte 1 (AO = V1H) the device identifier code. For theSGS-THOMSON ST27256P, these two identifierbytes are given below.All identifiers for manufacturer and device codeswill possess odd parity, with the MSB (07) definedas the parity bit.ELECTRONIC SIGNATURE MODE~IDENTIFIERAO 07 06(10) (19) (18)MANUFACTURER CODE VIL 0 0DEVICE CODE VIH 0 005 04 03 02 01 00 Hex(17) (16) (15) (13) (12) (11) Data1 0 0 0 0 0 200 0 0 1 0 0 046/10170