[Diy_efi] RE: looking for help with a prom N82S181

Steve Ravet Steve.Ravet at arm.com
Tue Nov 9 19:10:16 GMT 2004

Here's the pinout of your 2716:

 1 -|a7             vcc|- 24
 2 -|a6              a8|- 23
 3 -|a5              a9|- 22
 4 -|a4             vpp|- 21
 5 -|a3             /oe|- 20
 6 -|a2     2716    a10|- 19
 7 -|a1             /ce|- 18
 8 -|a0              o7|- 17
 9 -|o0              o6|- 16
10 -|o1              o5|- 15
11 -|o2              o4|- 14
12 -|gnd             o3|- 13

Here's the pinout of the N82S181:

 1 -|a7             vcc|- 24
 2 -|a6              a8|- 23
 3 -|a5              a9|- 22
 4 -|a4            nCE1|- 21
 5 -|a3            nCE2|- 20
 6 -|a2   N82S181   CE3|- 19
 7 -|a1             CE4|- 18
 8 -|a0              o7|- 17
 9 -|o0              o6|- 16
10 -|o1              o5|- 15
11 -|o2              o4|- 14
12 -|gnd             o3|- 13

There are a couple problems here.

Pin 21 nCE1 (vpp):  The trace shows this signal toggling.  vpp=3Dgnd is =
not listed in the datasheet (ST microelectronics) that I'm looking at.  =
vpp should always be either Vcc (5V) or Vpp (25V).  connecting it to =
ground may be OK, or it may keep it from working, or it may damage the =
device.  Assuming you don't want to program the chip in circuit, then =
wire this pin to Vcc.

pin 22 nCE2 (/oe):  In 2716 read mode this pin is equivalent to the PROM =
nCE2 so this pin is OK.

pin 23 CE3 (a10):  toggles continuously in your trace.  CE3=3Da10=3DVcc =
is OK (will read from the upper half of the EPROM).  But CE3=3Da10=3DGND =
is not OK.  In this case the PROM would be tristated but the EPROM will =
drive data onto the output bus, potentially conflicting with another =

pin 24 CE4 (/ce):  seems to be permanently wired to Vcc to enable the =
PROM.  Vcc on this pin will permanently disable the EPROM.

*IF* you can determine that CE4 is always driven high, ie connected to =
VCC, then a simple way to fix pins 23 and 24 is to wire pin 23 on the =
EPROM (a10) to ground, and to invert the signal at the pin 23 pad and =
then connect that to pin 24 of the EPROM (/ce)

If CE4 is driven by logic then you still have to connect EPROM pin a10 =
to ground, then OR the pin 23 and pin 24 pad values, invert that, and =
connect to EPROM pin 24.

hope that makes sense,


> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org=20
> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of=20
> mbelloli at speedymotorsports.com
> Sent: Monday, November 08, 2004 11:16 PM
> To: diy_efi at diy-efi.org
> Cc: hexibot43 at yahoo.com
> Subject: [Diy_efi] RE: looking for help with a prom N82S181
>      I realized I needed to give more information to go with=20
> my question.=20
> I have included a link to a web page I created.  I included=20
> some pics from my DSO of the signals on the 4 chip enable=20
> pins.  I am hoping someone can look at this a give me a clue.=20
>  I'm feeling pretty clueless right now.  I'm not=20
> understanding the what I'm seeing.  I especially don't=20
> understand  what I am seeing on pin 19.  It looks like noise to me.
>      Tomorrow, I'm going to look at the chip enable pin on a=20
> 27c256 I have in another ecm.  I am hoping to get a clue from=20
> this.  But if anyone has anything to add, please let me know.=20
>  I thought this was going to be so simple.
> Thanks,
> Marcello
> Here is the link to a page with the pic's.
> http://home.comcast.net/~hexibot43/MarcellosPage.htm

diy_efi mailing list
diy_efi at diy-efi.org

More information about the Diy_efi mailing list