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Using Flash RAM to replace obsolete CMOS RAM

Started by John Robertson June 29, 2021
I have a project in mind using small Flash RAM and a cheap CPU to 
substitute for the old TTL level CMOS RAM used on arcade games.

This has come up because the NVRAM that is currently being used is 
getting hard to find at prices under $7 to $9USD.

Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are 
$0.20 in single quantities.

The size of CMOS RAM we are replacing ranges from 512 x 4 (yeah, 512 
bits) up to 256K x 8 (perhaps the AT25SF041B-SHB-T?).

Granted this will take a bit of programming but I don't know if it is 
possible to start with before I want to invest any time/money into this 
project. I mean we can use batteries until the current shortage in NVRAM 
is over, but that isn't as much fun.

Also, we need to get past the doom & gloom crap I'm seeing here.

John ;-#)#

-- 
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
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                      www.flippers.com
        "Old pinballers never die, they just flip out."
John Robertson wrote:
> I have a project in mind using small Flash RAM and a cheap CPU to > substitute for the old TTL level CMOS RAM used on arcade games. > > This has come up because the NVRAM that is currently being used is > getting hard to find at prices under $7 to $9USD. > > Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are > $0.20 in single quantities. > > The size of CMOS RAM we are replacing ranges from 512 x 4 (yeah, 512 > bits) up to 256K x 8 (perhaps the AT25SF041B-SHB-T?). > > Granted this will take a bit of programming but I don't know if it is > possible to start with before I want to invest any time/money into this > project. I mean we can use batteries until the current shortage in NVRAM > is over, but that isn't as much fun. > > Also, we need to get past the doom & gloom crap I'm seeing here. >
What sort of cycle times do you need? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
On 6/29/2021 10:19 AM, John Robertson wrote:
> I have a project in mind using small Flash RAM and a cheap CPU to substitute > for the old TTL level CMOS RAM used on arcade games.
Are you thinking that the CPU could intercept the read/write accesses to the "original device" and emulate them via its flash? Not likely.
> This has come up because the NVRAM that is currently being used is getting hard > to find at prices under $7 to $9USD.
Is it true NVRAM (e.g., MNOS devices) or BBSRAM?
> Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are $0.20 > in single quantities. > > The size of CMOS RAM we are replacing ranges from 512 x 4 (yeah, 512 bits) up > to 256K x 8 (perhaps the AT25SF041B-SHB-T?).
That's actually 2K bits (512x4) or 2Mbits (256Kx8).
> Granted this will take a bit of programming but I don't know if it is possible > to start with before I want to invest any time/money into this project. I mean
"Programming" *in* the module, you're not talking about butchering the code in the games...
> we can use batteries until the current shortage in NVRAM is over, but that > isn't as much fun.
You could make a "dead bug" module that plugs in place of the existing device. No CPU, just a bit of write-protect logic (to safeguard the contents as power fails). This is how we developed games (in the 70's) without having to constantly burn EPROMs. (we called them "pigs" as in "piggyback" -- as you'd stack two 2Kx8 devices and some logic to emulate a 4KB EPROM) We didn't worry about spanning power outages so you would have to add a coin cell to maintain the device's contents.
> Also, we need to get past the doom & gloom crap I'm seeing here.
On 2021/06/29 10:22 a.m., Phil Hobbs wrote:
> John Robertson wrote: >> I have a project in mind using small Flash RAM and a cheap CPU to >> substitute for the old TTL level CMOS RAM used on arcade games. >> >> This has come up because the NVRAM that is currently being used is >> getting hard to find at prices under $7 to $9USD. >> >> Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips >> are $0.20 in single quantities. >> >> The size of CMOS RAM we are replacing ranges from 512 x 4 (yeah, 512 >> bits) up to 256K x 8 (perhaps the AT25SF041B-SHB-T?). >> >> Granted this will take a bit of programming but I don't know if it is >> possible to start with before I want to invest any time/money into >> this project. I mean we can use batteries until the current shortage >> in NVRAM is over, but that isn't as much fun. >> >> Also, we need to get past the doom & gloom crap I'm seeing here. >> > > What sort of cycle times do you need? > > Cheers > > Phil Hobbs >
These boards all run pretty much under 5mhz, most are <1mhz. Access times are typically around 100ns with older (mid-late 70s - 5101 for example) parts around 250ns. John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
On 6/29/2021 1:19 PM, John Robertson wrote:
> I have a project in mind using small Flash RAM and a cheap CPU to > substitute for the old TTL level CMOS RAM used on arcade games. > > This has come up because the NVRAM that is currently being used is > getting hard to find at prices under $7 to $9USD. > > Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are > $0.20 in single quantities. > > The size of CMOS RAM we are replacing ranges from 512 x 4 (yeah, 512 > bits) up to 256K x 8 (perhaps the AT25SF041B-SHB-T?). > > Granted this will take a bit of programming but I don't know if it is > possible to start with before I want to invest any time/money into this > project. I mean we can use batteries until the current shortage in NVRAM > is over, but that isn't as much fun. > > Also, we need to get past the doom & gloom crap I'm seeing here. > > John ;-#)# >
Alliance still has some 256k, 512, 1Mbit 70ns srams available in DIP for like $3.50 - $5: <https://www.mouser.com/Alliance-Memory/Semiconductors/Memory-ICs/SRAM/_/N-4bzpt?P=1z0z63xZ1yzswq7&Ns=Pricing%7c0>
John Robertson <spam@flippers.com> wrote:
> I have a project in mind using small Flash RAM and a cheap CPU to > substitute for the old TTL level CMOS RAM used on arcade games. > > This has come up because the NVRAM that is currently being used is > getting hard to find at prices under $7 to $9USD. > > Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are > $0.20 in single quantities.
It is not "Flash RAM"! It is "NOR Flash". You can use that to store firmware or read-only data, you cannot write and read single bytes like in a normal RAM but only large blocks of data can be erased and then re-programmed much like an EEPROM.
On 2021/06/29 12:29 p.m., Rob wrote:
> John Robertson <spam@flippers.com> wrote: >> I have a project in mind using small Flash RAM and a cheap CPU to >> substitute for the old TTL level CMOS RAM used on arcade games. >> >> This has come up because the NVRAM that is currently being used is >> getting hard to find at prices under $7 to $9USD. >> >> Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are >> $0.20 in single quantities. > > It is not "Flash RAM"! > It is "NOR Flash". You can use that to store firmware or read-only > data, you cannot write and read single bytes like in a normal RAM but > only large blocks of data can be erased and then re-programmed much > like an EEPROM. >
Thanks for pointing that out. That type of part is useless for my needs then. Oh well, back to the drawing board! John :-#(# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
On 6/29/2021 2:20 PM, John Robertson wrote:
> On 2021/06/29 12:29 p.m., Rob wrote: >> John Robertson <spam@flippers.com> wrote: >>> I have a project in mind using small Flash RAM and a cheap CPU to >>> substitute for the old TTL level CMOS RAM used on arcade games. >>> >>> This has come up because the NVRAM that is currently being used is >>> getting hard to find at prices under $7 to $9USD. >>> >>> Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are >>> $0.20 in single quantities. >> >> It is not "Flash RAM"! >> It is "NOR Flash". You can use that to store firmware or read-only >> data, you cannot write and read single bytes like in a normal RAM but >> only large blocks of data can be erased and then re-programmed much >> like an EEPROM. > > Thanks for pointing that out. > > That type of part is useless for my needs then. > > Oh well, back to the drawing board!
No, you use RAM (in the MCU) to cache data from the FLASH, reading *and* writing. You then move *updated* data from the cache back into FLASH to give you the non-volatility. This lets you live with the page updates imposed by the FLASH as well as adapt to its limited durability (R/W cycles). Easy peasey. The problem is that you can't easily have the MCU respond to activity at the rate that the "host" CPU undertakes (you can't "wait state" the host CPU because NVRAMs don't have "wait" signals -- unless you are emulating FLASH! :> )
On 6/29/2021 2:20 PM, John Robertson wrote:
> On 2021/06/29 12:29 p.m., Rob wrote: >> John Robertson <spam@flippers.com> wrote: >>> I have a project in mind using small Flash RAM and a cheap CPU to >>> substitute for the old TTL level CMOS RAM used on arcade games. >>> >>> This has come up because the NVRAM that is currently being used is >>> getting hard to find at prices under $7 to $9USD. >>> >>> Something like the M25P05-AVMN6P (512k or 64K x 8) or similar chips are >>> $0.20 in single quantities. >> >> It is not "Flash RAM"! >> It is "NOR Flash". You can use that to store firmware or read-only >> data, you cannot write and read single bytes like in a normal RAM but >> only large blocks of data can be erased and then re-programmed much >> like an EEPROM. > > Thanks for pointing that out. > > That type of part is useless for my needs then. > > Oh well, back to the drawing board!
No, you use RAM (in the MCU) to cache data from the FLASH, reading *and* writing. You then move *updated* data from the cache back into FLASH to give you the non-volatility. This lets you live with the page updates imposed by the FLASH as well as adapt to its limited durability (R/W cycles). Easy peasey. The problem is that you can't easily have the MCU respond to activity at the rate that the "host" CPU undertakes (you can't "wait state" the host CPU because NVRAMs don't have "wait" signals -- unless you are emulating FLASH! :> )
On 6/29/2021 3:10 PM, Don Y wrote:

apologies for the second post; nntp client returned fail on first!