Re: SD I/O 1.8MHz resonator
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The 8250 has a coarse divider for baud rate.?
12 works to divide 1,843,200 to 9600 baud because
1843200 / 12 / 16 = 9600
The next divider number is 13 and to get 9600 at that value you would need...
X / 13 / 16 = 9600
Solve for X = 1,996,800? ?(so 2Mhz would be pretty decent)
2Mhz gives 9615, = 0.2% error
But, as pointed out, 1.8 is available and 1.8432 crystals will also work (adding the loading caps).
On Friday, April 30, 2021, 04:22:10 p.m. EDT, Lee Hart <leeahart@...> wrote:
Zanchius wrote:
> I would be comfortable in flipping a byte or two on the EPROM image, I
> managed to find a programmer that can burn 27256 chips so that also
> wouldn't be an issue.
> May I ask which bytes should be changed?
Hi Flavio,
Download the EPROM source file at
<> from the website at
<>.
In the .ASM or .LST file, search for "LD (ACE_BAUD),A". It occurs in two
places. The first one sets the initial baud rate to 9600 (with a 1.8 MHz
resonator or 1.8432 crystal). Change the byte at 01AE to whatever is
correct for your crystal and desired baud rate.
01A5? 21 80FF??? COLD_START??? LD??? HL,RC_TYPE
01A8? 06 0F??? ??? ??? LD??? B,CS_CLR_LEN
01AA? CD 100C??? ??? ??? CALL??? CLEAR_BLOCK
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_TYPE)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_SOFT)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_STEP)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_CC)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_HALT)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_F0)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_RST0)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RC_HARD)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RegPtr)
? ? ? ? ? ? ? ??? ??? ??? ;DW??? 0??? ;(ABUSS)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(IoPtr)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RX_ERR_LDRT)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RX_ERR_STOP)
? ? ? ? ? ? ? ??? ??? ??? ;DB??? 0??? ;(RX_ERR_OVR)
01AD? 3E 0C? ??? ??? ??? LD??? A,12 <=== this sets 9600 baud!
01AF? 32 8FFF? ? ? ? ? ??? ??? LD??? (ACE_BAUD),A
Or, if you're using the Z80-CPU card serial port, you can change the
Z80-SIO card baud rate using this call:
080B? CD CA0D? ? ? ? ? PORT_SPEED??? CALL??? PRINTI??? ???
080E? 0D0A2830 433D3936 ??? ??? DB??? CR,LF,"(0C=9600) BAUD:",EOS
0816? 30302920 42415544
081E? 3A00
0820? 3A 8FFF? ? ? ? ? ??? ??? LD??? A,(ACE_BAUD)
0823? CD F60D? ? ? ? ? ??? ??? CALL??? PUT_BYTE
0826? CD 490D? ? ? ? ? ??? ??? CALL??? SPACE_GET_BYTE
0829? D8? ? ? ? ? ? ? ? ??? ??? RET? C
082A? 32 8FFF? ? ? ? ? ??? ??? LD??? (ACE_BAUD),A
082D? CD F214? ? ? ? ? ??? ??? CALL??? ACE_SET_BAUD
0830? C9? ? ? ? ? ? ? ? ??? ??? RET
Hope this helps!
Lee
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
? ? ? ? -- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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