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Read/Write Socket for USE in a Read-Only Socket for an EPROM

IP.com Disclosure Number: IPCOM000043473D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Combs, JL: AUTHOR

Abstract

A read-only socket includes eleven address lines A0-A10, a CE* control line, which is low when reading from an EPROM (eraseable programmable read-only memory), and an OE* control line, which is used to enable reading from the EPROM. By the use of three latches 74LS374 and a decoder 74LS138, a read-write socket can be connected to the read-only socket to enable both reading and writing of a 2716 EPROM. The eight address lines A0-A7 of the read-only socket are used for all data and address lines of the read-write socket. As shown in Figs. 1A and 1B, the read-write socket has data lines D0-D7, address lines A0-A10, a voltage line Vpx, an OE* control line, and a CE* control line. Pins 9 and 12 of one of the three 74LS374 latches are not used.

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Read/Write Socket for USE in a Read-Only Socket for an EPROM

A read-only socket includes eleven address lines A0-A10, a CE* control line, which is low when reading from an EPROM (eraseable programmable read-only memory), and an OE* control line, which is used to enable reading from the EPROM. By the use of three latches 74LS374 and a decoder 74LS138, a read-write socket can be connected to the read-only socket to enable both reading and writing of a 2716 EPROM. The eight address lines A0-A7 of the read-only socket are used for all data and address lines of the read-write socket. As shown in Figs. 1A and 1B, the read-write socket has data lines D0-D7, address lines A0-A10, a voltage line Vpx, an OE* control line, and a CE* control line. Pins 9 and 12 of one of the three 74LS374 latches are not used. When programming the 2716 EPROM, it is necessary to have a voltage of +25 volts while the operating voltage for the 2716 EPROM is 5 volts. The circuit of Fig. 2, which is part of the read-write socket, converts Vpx to Vpp of 5 or 25 volts depending on whether Vpx is high or low. Fig. 3 is a timing diagram showing the states at various times for a programming sequence as follows, with the read-write socket inserted in the read-only socket: State 0 - Set CE* = 1 OE* = 1

Vpx = 0

Insert EPROM.

1 - Set CE* = 0

OE* = 1

Vpx = 0

2 - Set CE* = 0

OE* = 1

Vpx = 1

3 - Set Low Address (A0 - A7)

4 - Set High Address (A8 - A10)

5 - Set Data

6 - Set CE* = 1

OE* = 1

Vpx = 1

----------------- Wait 50 milliseconds.

7 - Set CE* = 0

OE* = 1

Vpx = 1

----------------- Repeat states 3,4,5,6,7

until completed.

8 - Set CE* = 0

OE* = 1

Vpx = 0

9 - Set CE* = 1

OE* = 1

Vpx = 0

----------------- Remove read-write socket

with EPROM from read-only

socket and replace with EPROM. The

1

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following are software routines to write into the 2716 EPROM when the 2716 EPROM is inserted into the read-write socket of Fig. 1: This routine will send data in the accumulator to the data latch. DATAOUTPUSH H ;SAVE H&L REGISTER PAIR MOV L,A ;PUT DATA IN LOWER ADDRESS BUS

MVI H,BASE ;SET UPPER PORTION OF ADDRESS

FOR PROPER DECODE

MOV A,M ;DO "WRITE"

POP H ;RESTORE REGISTERS

RET ;RETURN TO CALLER This routine will send the lower address to the lower address latch. The lower address data must be in the accumulator. LADDOUTPUSH H ;SAVE H&L REGISTER PAIR MOV L,A ;PUT LOWER ADDRESS DATA IN

LOWER ADDRESS BUS

MVI H,BASE+1 ;SET UPPER PORTION OF ADDRESS

FOR PROPER DECODE

MOV A,M ;DO "WRITE"

POP H ;RESTORE R...