AM28F256A_95 查看數據表（PDF） - Advanced Micro Devices

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AM28F256A_95

256 Kilobit (32,768 x 8-Bit) CMOS 12.0 Volt, Bulk Erase Flash Memory with Embedded Algorithms

Advanced Micro Devices 

AMD

READ ONLY MODE

VPP < VCC + 2 V

Command Register Inactive

Read

The Am28F256A functions as a read only memory when

VPP < VCC + 2 V. The Am28F256A has two control func-

tions. Both must be satisfied in order to output data. CE

controls power to the device. This pin should be used for

specific device selection. OE controls the device out-

puts and should be used to gate data to the output pins if

a device is selected.

Address access time tACC is equal to the delay from sta-

ble addresses to valid output data. The chip enable ac-

cess time tCE is the delay from stable addresses and

stable CE to valid data at the output pins. The output en-

able access time is the delay from the falling edge of OE

to valid data at the output pins (assuming the addresses

have been stable at least tACC – tOE).

Standby Mode

The Am28F256A has two standby modes. The CMOS

standby mode (CE input held at VCC ± 0.5 V), consumes

less than 100 µA of current. TTL standby mode (CE is

held at VIH) reduces the current requirements to less

than 1 mA. When in the standby mode the outputs are in

a high impedance state, independent of the OE input.

If the device is deselected during erasure, program-

ming, or program/erase verification, the device will draw

active current until the operation is terminated.

Output Disable

Output from the device is disabled when OE is at a logic

high level. When disabled, output pins are in a high

impedance state.

Auto Select

Flash memories can be programmed in-system or in a

standard PROM programmer. The device may be sol-

dered to the circuit board upon receipt of shipment and

programmed in-system. Alternatively, the device may

initially be programmed in a PROM programmer prior to

soldering the device to the board.

The Auto select mode allows the reading out of a binary

code from the device that will identify its manufacturer

and type. This mode is intended for the purpose of

automatically matching the device to be programmed

with its corresponding programming algorithm. This

mode is functional over the entire temperature range of

the device.

Programming In A PROM Programmer

To activate this mode, the programming equipment

must force VID (11.5 V to 13.0 V) on address A9. Two

identifier bytes may then be sequenced from the device

outputs by toggling address A0 from VIL to VIH. All other

address lines must be held at VIL, and VPP must be less

than or equal to VCC + 2.0 V while using this Auto select

mode. Byte 0 (A0 = VIL) represents the manufacturer

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

the Am28F256A these two bytes are given in the table

below. All identifiers for manufacturer and device codes

will exhibit odd parity with the MSB (DQ7) defined as the

parity bit.

(Refer to the AUTO SELECT paragraph in the ERASE,

PROGRAM, and READ MODE section for program-

ming the Flash memory device in-system).

Type

Manufacturer Code

Device Code

Table 2. Am28F256A Auto Select Code

Code

A0 (HEX) DQ7 DQ6 DQ5 DQ4

VIL

01

0

0

0

0

VIH

2F

0

0

1

0

DQ3

0

1

DQ2

0

1

DQ1

0

1

DQ0

1

1

Am28F256A

2-43

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