Pin count difference - DM74S573N - Page 1
Forum section: electronics / beginners

author: bitman
author_rank: Unknown
timestamp: February 18, 2018, 01:37:30 am
content: What am I reading wrong here on the chip - I read this as a DM74S573N which I have the data-sheet for herehttp://pdf1.alldatasheet.com/datasheet-pdf/view/135427/NSC/DM74S573N.html. According to the data-sheet there should be 20 pins - but this chip only has 18? Color me confused - but I guess I shouldn't be surprised? I can find it listed on some sites for purchase as an 18pin chip - so I'm pretty sure I have the wrong data sheet, but this model is listed in the sheet and everything seems to match otherwise?

author: bitman
author_rank: Unknown
timestamp: February 18, 2018, 01:47:20 am
content: Hmmm - I found another datasheet that matches the chphttp://www.datasheets360.com/pdf/4783000051525452916. Question from the newbie is, if the model number is the same, how does this happen? What am I missing when I look up the datasheet?

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 18, 2018, 02:26:27 am
content: I looked in the 1977, 1980, and 1990 National databooks. 18 pins in all cases. I did find a 20-pin datasheet on the web.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 05:25:32 am
content: Here : Section 3-27 page 228 0n PDF readerhttp://bitsavers.informatik.uni-stuttgart.de/components/national/_dataBooks/1987_Non-Volatile_Memory_Databook.pdf18 pin DM54/74S573A

author: 2N3055
author_rank: Super Contributor
timestamp: February 18, 2018, 10:15:55 am
content: 74x57318 pin one is old 4096-BIT TTL PROM by NS..20 pin one is Octal D-type transparent latch; 3-state...Yeah, there are many instances in industry when they used same numbers for different stuff...

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 03:53:08 pm
content: Well that's odd, the block diagram in OPs datasheet is showing 16 connections.if you add the Vcc and ground that would make 18 .Its missing Q4,Q5,Q6 and Q7.

author: glarsson
author_rank: Frequent Contributor
timestamp: February 18, 2018, 04:22:22 pm
content: Quote from: Jwillis on February 18, 2018, 03:53:08 pmWhy is it odd that a 1k*4 PROM only has four data outputs (Q0 - Q3)? Why do you expect it to have Q4, Q5, Q6 and Q7?

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 04:35:05 pm
content: Quote from: glarsson on February 18, 2018, 04:22:22 pmJust that the pin outs are showing Q4-Q7 on pins 11,12,13,14

author: glarsson
author_rank: Frequent Contributor
timestamp: February 18, 2018, 06:41:38 pm
content: Quote from: Jwillis on February 18, 2018, 04:35:05 pmBut that pinout is for the 20-pin version that is not a PROM. The data sheet is about the 18-pin PROM, except the pinout on page 2.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 06:59:08 pm
content: Don't get wrong.It's not my intention to argumentative.I was just wondering why they would present a data sheet like that.It just causes confusion.

author: stj
author_rank: Super Contributor
timestamp: February 19, 2018, 08:39:11 am
content: you are confusing a 74s573 with a 74ls573.an easy mistake given that there used to be a schottky version of ttl called 74s, before low power schottky (74ls) was developed.unfortunatly 74s was also used to designate bipolar rom by a couple of manufacturers.not all, some used different prefixes to avoid this confusion.

author: newbrain
author_rank: Super Contributor
timestamp: February 19, 2018, 03:59:44 pm
content: Quote from: glarsson on February 18, 2018, 06:41:38 pmActually, if look at the DS in the OP first post (but not in any other I could find online), you'll see that on page two a 20-pin pinout is shown.That pinout, though, seems to be for a 512x8 bits memory (still 4096bits), such as maybe a DM54S472, so it has only 9 address lines but 8 data lines.Probably an early, wrong, version of the datasheet.

author: Jwillis
author_rank: Super Contributor
timestamp: February 20, 2018, 11:25:59 am
content: Maybe my first reply was confusing but here is the datasheet.

author: newbrain
author_rank: Super Contributor
timestamp: February 20, 2018, 12:46:44 pm
content: Quote from: Jwillis on February 20, 2018, 11:25:59 amAn here is the "funny" one with 20pins...which is of course wrong!