HT27C020 datasheet(6/11 Pages) HOLTEK

6 / 11 page

Functional Description

Programming of the HT27C020

When the HT27C020 is delivered, the chip has

all 2048K bits in the “ONE”, or HIGH state.

“ZEROs” are loaded into the HT27C020 through

programming.

The programming mode is entered when

12.5

±0.2V is applied to the VPP pin, OE is at VIH,

and CE and PGM are VIL. For programming, the

data to be programmed is applied with 8 bits in

parallel to the data pins.

The programming flowchart in Figure 3

shows the fast interactive programming algo-

rithm. The interactive algorithm reduces pro-

gramm ing tim e by using 30

µs to 105µs

programming pulses and giving each address

only as many pulses as is necessary in order to

reliably program the data. After each pulse is

applied to a given address, the data in that

address is verified. If the data is not verified,

additional pulses are given until it is verified

or until the maximum number of pulses is

reached while sequencing through each ad-

dress of the HT27C020. This process is re-

peated while sequencing through each address

of the HT27C020. This part of the program-

ming algorithm is done at VCC=6.0V to assure

that each EPROM bit is programmed to a suf-

ficiently high threshold voltage. This ensures

that all bits have sufficient margin. After the

final address is completed, the entire EPROM

memory is read at VCC=VPP=5.25

±0.25V to ver-

ify the entire memory.

Program inhibit mode

Programming of multiple HT27C020 in parallel

with different data is also easily accomplished by

using the Program Inhibit Mode. Except for CE,

all like inputs of the parallel HT27C020 may be

common. A TTL low-level program pulse applied to

an HT27C020 CE input with Vpp=12.5

±0.2V, PGM

LOW, and OE HIGH will program that HT27C020.

A high-level CE input inhibits the HT27C020 from

being programmed.

Program verify mode

Verification should be performed on the pro-

grammed bits to determine whether they were

correctly programmed. The verification should

be performed with OE and CE at VIL, PGM at

VIH, and VPP at its programming voltage.

Auto product identification

The Auto Product Identification mode allows

the reading out of a binary code from an

EPROM that will identify its manufacturer and

the type. This mode is intended for program-

ming to automatically match the device to be

programmed with its corresponding program-

ming algorithm. This mode is functional in the

°C±5°C ambient temperature range that is

required when programming the HT27C020.

To activate this mode, the programming equip-

ment must force 12.0

±0.5V on the address line A9

of the HT27C020. Two identifier bytes may then

be sequenced from the device outputs by toggling

address line A0 from VIL to VIH, when A1=VIH. All

other address lines must be held at VIH during

Auto Product Identification mode.

Byte 0 (A0=VIL) represents the manufacturer

code, and byte 1 (A0=VIH), the device code. For

HT27C020, these two identifier bytes are given in

the Operation mode truth table. All identifiers for

the manufacturer and device codes will possess

odd parity, with the MSB (DQ7) defined as the

parity bit. When A1=VIL, the HT27C020 will read

out the binary code of 7F, continuation code, to

signify the unavailability of manufacturer ID

codes.

Read mode

The HT27C020 has two control functions, both

of which must be logically satisfied in order to

obtain data at outputs. Chip Enable (CE) is the

power control and should be used for device

selection. Output Enable (OE) is the output

control and should be used to gate data to the

output pins, independent of device selection.

Assuming that addresses are stable, address

access time (tACC) is equal to the delay from CE

HT27C020

10th May ’99

HT27C020 Datasheet(PDF) 6 Page - Holtek Semiconductor Inc

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