(OT) ZN448E ADC chip

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Aug 29 17:54:00 2003

> On Aug 28, 22:39, Tony Duell wrote:
> > > It's over 10 years old, and it's microprocessor-compatible, but
> it's an
> > > analogue to digital converter chip, not a computer. It's also not
> in
> > > my spares box, and I need one. Does anyone have a spare? Or a
> data
> > > sheet?
> >
> > I can't find a chip (although it sounds familiar for some reason),
> but I
> > do have a Ferranti data book that covers it. What do you need to
> know?
>
> Pinout, and if possible some timing info (conversion time etc) and what

Firstly, the ZN447, ZN448, and ZN449 are all much the same apart from
linearity errors. So if you can find data on any of them it'll be of use.

The pinout is (18 pin DIL):

1 : Busy/ (End of Conversion)
2: RD/ (Output Enable)
3 : Clcok
4 : Wr/ (Start Conversion)
5 : Rext (End of comparator tail, via resistor to -5V or so)
6 : Vin (Input)
7 : VRef In (Reference Input)
8 : VRef Out ( 2.5V reference output, often strapped to pin 7)
9 : Ground
10 : Vcc (+5V)
11 : DB7 (MSB)
12 : DB6
13 : DB5
14 : DB4
15 : DB3
16 : DB2
17 : DB1
18 : DB0 (LSB)

The clock is either : A cap from 3 to ground (tup something between 100pF
and 1nF to start with), a RC series circuit from 3 to ground, a network
consisting of ((1MHz Xtal in series with 56pf) in parallel with (2n2 in
series with 4k7)), or a TTL level clock signal.

The reference is basically a 2.5V 'zener' between 8 and ground. You need
to connect a resistor (390R is shown) from 8 to Vcc, and a 4u7 cap from 8
to ground is a good idea. This will give a 2.5V reference.

You can use an external reference of a volateage between 1.5V and 3V. You
can actually go below 1.5V, but the device gets slower (!).

COnversion time is 7.5 to 8.5 clock cycles, the clock frequency is
somewhere between 100kHz and 1MHz with the values I suggested.

-tony
Received on Fri Aug 29 2003 - 17:54:00 BST