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#1 23-03-2010 17:08:58
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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 18:24:44
- cdesp
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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 22:49:32
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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 22:49:57)
#4 05-06-2010 13:58:17
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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 13:39:35
- cdesp
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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 14:58:57)
#6 29-07-2010 17:04:14
- cdesp
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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.
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