english greek
Home arrow Forum

The Newbrain Forum

Anything about the Newbrain Home Computer

You are not logged in.

Add to: Mr. Wong Add to: Webnews Add to: Icio Add to: Oneview Add to: Folkd Add to: Yigg Add to: Linkarena Add to: Digg Add to: Del.icio.us Add to: Reddit Add to: Simpy Add to: StumbleUpon Add to: Slashdot Add to: Netscape Add to: Furl Add to: Yahoo Add to: Spurl Add to: Google Add to: Blinklist Add to: Blogmarks Add to: Diigo Add to: Technorati Add to: Newsvine Add to: Blinkbits Add to: Ma.Gnolia Add to: Smarking Add to: Netvouz Information

#1 23-03-2010 18:08:58

admin
Administrator

(Hover for details)
Registered: 01-01-1970
Posts: 12
Reputation :   

Serial

I have the schematics for this one but have not implemented yet.
I am trying to find a 16c550 Uart .
Any other suggestion using a newer IC is very welcome.

 

#2 07-04-2010 19:24:44

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: Serial

A newer chip from Maxim the
MAX3100CPD - MAX3100 SPI Compatible UART uses SPI/MICROWIRE Interface to the cpu.

The MAX3100 combines a simple UART and a baudrate
generator with an SPI interface and an interrupt
generator. Configure the UART by writing a 16-bit word
to a write-configuration register, which contains the
baud rate, data-word length, parity enable, and enable
of the 8-word receive first-in/first-out (FIFO). The write
configuration selects between normal UART timing and
IrDA timing, controls shutdown, and contains 4 interrupt
mask bits.

Seems ok to me maybe a little bit more programming to make it work.

 

#3 12-04-2010 23:49:32

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: Serial

I found a source for the 16c550CN (40 pin DIP) I.C. on ebay and i order 3 pieces.
So i now wait for them to arrive from Hong Kong.

Last edited by cdesp (12-04-2010 23:49:57)

 

#4 05-06-2010 14:58:17

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: Serial

Hi,
Yesterday i finally got the 14,7456MHz crystal that is needed for the 16550 to work.
And today the serial connection is working.

Something that took me some time to find out:
For 1.8432MHz crystal the divisor for the UART should be 12 to have 9600bps according to datasheet.
So for 14,7456MHz should be 96 but instead i found out after many hours that it gives 7200bps
Now either my crystal circuit gives some other freq or something else is wrong.

 

#5 08-06-2010 14:39:35

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: Serial

If someone can help with this:

As i said the crystal i use is 14,7456MHz and in order to oscillate i use this circuit:
http://www.gaby.de/z80/gfx/series.gif

So it should give 14,7456MHz instead since my divisor is 72 and it turns out that in order to communicate my terminal should be set at 4800bps that the frequency is 5,5296MHz????? now how is this possible i don't know.

since i don't  have an oscilloscope i can't debug the circuit and in order to find out the baud rate i had to experiment a lot giving different buad rates in my terminal program an see what it shows.

Because i use the same circuit for the 16 Mhz crystal for the main freq of z80 i must assume that z80 is not running at 4MHz as i thought.


Regards,

Chris

P.S.

Instead of 330 Ohm resistor i use 1K4
if i change the resistors it changes the way the crystal oscillates(or not at all).

Last edited by cdesp (08-06-2010 15:58:57)

 

#6 29-07-2010 18:04:14

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: Serial

I gave up with the oscillation circuit so i just bought oscillators instead of crystals.
Anyway the RS232 PCB board is ready but untested.

 


Add to: Mr. Wong Add to: Webnews Add to: Icio Add to: Oneview Add to: Folkd Add to: Yigg Add to: Linkarena Add to: Digg Add to: Del.icio.us Add to: Reddit Add to: Simpy Add to: StumbleUpon Add to: Slashdot Add to: Netscape Add to: Furl Add to: Yahoo Add to: Spurl Add to: Google Add to: Blinklist Add to: Blogmarks Add to: Diigo Add to: Technorati Add to: Newsvine Add to: Blinkbits Add to: Ma.Gnolia Add to: Smarking Add to: Netvouz Information

Forum Tools

Board information

Board statistics
Total number of registered users: 95
Total number of topics: 88
Total number of polls: 0
Total number of posts: 333
User information
Newest registered user: thecelticfan
Registered users online: 3
Guests online: 618

Powered by Agora 1.0.4 Acropolis

© Copyright 2007 - 2008 Joomla Me!. All rights reserved.

Powered by Elxis - Open Source CMS.
Copyright (C) 2006-2017 Elxis.org. All rights reserved.