Re: [Amforth-devel] mega8 installation problem

[Feusag M. <feu...@go...>]

Hi,

I had the same problem and traced it to the baud rate calculation.

It turns out that there is a 7% error at 9600 baud with a 1MHz system clock
(see table 60 in the datasheet) and this is out of spec for you PC UART to
read.

I changed the baud rate on line 22 of template.asm to 4800 (0.2% error) and
everything was OK.

I have also prototyped the following change to armforth/words/usart.asm to
use the U2X double speed mechanism.
With this change the error at 9600 baud is 0.2% with a 1MHz clock and works
perfectly.

Index: usart.asm
===================================================================
--- usart.asm   (.../vendor/amforth/2.3/words/usart.asm)
+++ usart.asm   (.../trunk/forth/amforth/words/usart.asm)
@@ -81,7 +81,7 @@
   .dw XT_D2SLASH
   .dw XT_D2SLASH
   .dw XT_D2SLASH
-  .dw XT_D2SLASH
+;   .dw XT_D2SLASH                             ; We are going for 2X, so
remove one of these...
   .dw XT_ROT
   .dw XT_UMSLASHMOD
   .dw XT_SWAP
@@ -96,7 +96,14 @@
   .dw XT_DOLITERAL
   .dw BAUDRATE0_HIGH
   .dw XT_CSTORE
+
   .dw XT_DOLITERAL
+  .dw $02                                              ; U2X
+  .dw XT_DOLITERAL
+  .dw $2B                                              ; UCSRA
+  .dw XT_CSTORE
+
+  .dw XT_DOLITERAL
   .dw (1<<UMSEL01)|(3<<UCSZ00)
   .dw XT_DOLITERAL
   .dw USART0_C



I hope this helps.

Cheers

Feusag