Hi,

I need a POWER GOOD circuit to protect data stored in a CMOS RAM and in a RTC powerd by a Ni-Cd battery, during startup and shutdown of my 6502 based board. Can anyone help me?

Fabio

Fabio,

Have you looked into using any of the Maxim chips? They make a number of "microprocessor supervisory" chips that will do what you need in a single-chip solution. You can find complete info on the at http://www.maxim-ic.com and they'll probably even send you free samples of the chips you're interested in.

_________________
- Mike Naberezny (mike@naberezny.com) http://6502.org

In my computer, I used a MAX1691 supervisory circuit which I received as a free sample.This incorporates an integrated 3V Li battery for battery backup RAM, switchover logic for battery backup RAM( adding only 7 ns propagation delay to CS),Power-on/brownout reset, watchdog and powerfail NMI.The signal outputs of this chip remain valid well below 5 V which was important for me.The only drawback was the absence of open-collector type RESET\ signal- I made up for this by inverting the RESET signal(OC) with a BS 170 FET.

Also check out MAX 3100. This is a SPI UART chip which can be added to 6502 systems very easily. Using only 4 lines of 6522, one gets a 230 kbps serial I/O + RTS/CTS(with 8 bytes FIFO), software selectable IrDA mode and provision for 9 - bit networks. By simply using a RS485 interface chip in place of the normally used MAX 232,9 bit network facility allows several UARTs to be hooked up in a network with minimum CPU botheration.

Yes, Maxim does supply free samples!

I hadn't looked into those parts, but they sound nice. I'll have to check them out.

Maxim certainly does have a nice sample program. I can't tell you how many samples I've received from them for all kinds of specialty ICs. I get at least one package every month.

_________________
- Mike Naberezny (mike@naberezny.com) http://6502.org

>Maxim certainly does have a nice sample program

Of course. In fact, I have designed a periheral expansion board (connects to 6522 connector) for my computer using exclusively free sample ICs in addition to using ICs like MAX 1691,MAX 7555, MAX 662A(12 V for Flash programming) in the main board.I use-

MAX 350: to form a 8 slot SPI port using 5 port lines of 6522.
The slots are used as under:
MAX 3100 : 230 k SPI UART used in slot 1.The UART output can be switched between MAX 232(RS232 port) or MAX 3120(IrDA port)
MAX 3140 : SPI UART+prog. RS485 port in slot 2
25C040EN : EEPROM 4k bit (free sample- Fairchild)in slot 3.
I am not worried about the low capacity as there are similar pinout(8DIP) SPI EEPROMS upto 256K bits availble. Sooner or later a free sample is bound to be available
MAX 187 : 12 bit serial ADC in slot 4 for analogue measurements.
MAX 5156 : Dual 12 bit DAC in slot 5.
Slots 6,7,8 : future exp.
(I use slot 6 for driving a 2 x 16 LCD using 74ls164 sometimes - I purchased this IC!)

Two lines of 6522 are used for IIC interface. Presently I have provided 2 sockets for IIC EEPROM on this board and brought out the IIC lines on connector.A Fairchild free sample 24C17N (16kbits) EEPROM is being used on one of the sockets. Higher capacity IIC EEPROMS upto 256k bits with the same 8 DIP pinout are already available!

A lot of manufacturers are coming out with ICs for the IIC bus- say Dallas DS 1307 (8-DIP RTC), DS 1624(Digital thermometer + EEPROM) etc.

A free sample LM340AT5.0 P+ from National (5.0v,2%,1Amp) is also fitted in case I want to connect this board to a microcontroller port and supply it power also. Normally, I use Vcc supply from the main board - so the Vcc jumper is removed.

The PCB was designed using EAGLE layout freeware editor.

You might also look at the DALLAS SEMICONDUCTOR parts for this purpose. IIRC, there's a socket they call "intelligent, that's got a sensor for out-of-tolerance power which won't let the write line go low if power is out of tolerance.

There are lots of ways to skin this cat, but if you are just building one or a few, one of the "canned" solutions is probably best.

Uli

SLOHANI,

I'd like to incorporate a Maxim serial ADC into one of my existing 6502 boards. Can you give me some hints on getting started and maybe some source code for the serial protocol?

Thanks!

_________________
- Mike Naberezny (mike@naberezny.com) http://6502.org