I PROM

What is an IPROM?



IPROM is stand for Instantly Programmable Read Only Memory. The basic is to use a static RAM (Random Access Memory) with backup battery to replace the ROM purpose. Used a low power supply static RAM can hold the data until a year or more with 2 button batteries. And then, what for we use an IPROM to replace a conventional ROM? The data can not be changed in one or two byte in ROM. we must reprogramming all from the beginning, but in IPROM, even one byte can be changed. The fact also very indeed when we must make some test for a program under development. It is very hard and also tired to reprogramming the ROM times to times until the program run to the correct condition.

If we use an IPROM, we do not need an EPROM programmer or something like that, because the operation is to write like the standard RAM. In this circuit we use a RAM type HM6116LP (2k x 8 byte). It is enought for the small system computer. For the power, we can use one battery Ni-Cad like for CMOS backup or we can use 2 button cell batteries like LR-44 (in my proto-type, this type can hold data until a year). The construction need a quiet carefull to handel. The first, you must soldering all the componens to the PCB, and then assemble it one by one from the top to the bottom. Use a small one switch and a good type socket for the RAM IC's. For the complete circuit and construction, you can see the picture below:

click the below images for zooming 

 Fig.2. IPROM PCB.

Fig.1. IPROM Circuit.

  



          
                                   
                    

                      

Fig.3. IPROM Construction

Fig.4. IPROM View.

IPROM Part List :

• Resistors :
• R₁ = 220 Ohm
• R₂ = 56 Ohm
• R₃ = 1 kOhm
• R₄ = 4.7 kOhm
• R₅ = 2.2 kOhm (place when used a Ni-Cad battery for charging)
• R₆ ... R₂₆ = 47 kOhm
All resistors are ¹/₈ Watt type
• Capasitors :
• C1 = 4.7uF/16V (tantalum type)
• C2 = 10 nF (ceramic type)
• Semiconductors :
• D1 = Red LED
• D2, D3 = DUG (eg. 1N60, etc.)
• T1 = BC 547 B
• IC1 = HM 6116 LP
• IC2 = 4071 B
• Others :
• IC socket 24 pins = 2 pcs
• S1 = togle 1 pole
• 2 button cell battery or 1 Ni-Cad battery

When I create my PC program, I had to built the interface for the IPROM to run in my PC/XT. The circuit used an I/O address $E100:$0000 throught $E100:$0FFF for two IPROMs (you must canged it if you want to use it in the PC/AT computer, because that address has been used by the system ROM). The design is not quiet good because in that time it is very hard to find the two layer PCB and if can the value is to high, so I used it by combine the 2 type of PCBs. I used the ORCAD program and Smartwork to design the schematic and layout. For the slot, I used a two layer PCB, and for the IPROMs, I used a one layer PCB. The complete interface circuit is like below :

click the below images for zooming

 

 Interface Part List :

• Resistors :
• R₁ ... R₄ = 220 Ohm
• Semiconductors :
• IC₁ = 74LS07
• IC₂ = 74LS05
• IC₃ = 74LS32
• IC₄ ... IC₅ = IPROM
• IC₆ = 74LS245
• Capacitor :
• C₁, C₂ = 100nF
• Other :
• IC socket 24 pins = 2 pcs