kevinb@SDCSVAX.ARPA (12/30/85)
The CCS S-100 bus system CPU includes a small program in it's ROM for an
auto baud rate detection for console baud rate. When you boot, you hit the
return key 3 times and you're in A> prompt. I could try to get a copy of this
to you, to use as a source for developeing a driver for whatever comm program
you're using. Yes, please send code to the below address, I'll take a look at
it.
Kevin J. Belles - UUCP {sdcsvax,ihnp4!gould9,noscvax,cbosgd}!crash!kevinb
Disclaimer: Anything within, unless directly attributed is my opinion,
and does not reflect that of my place of employment. KjB@purdue.ARPA:mjs@purdue-ecn-ee.ARPA (mjs) (12/30/85)
Thanks for your quick reply. First of all, let me give you a little
background about this computer(Royal Alphatronic PC). According to Royal,
the only way to change the baud rate is by a hardwired jumper on the
main PCB. But, like I said, I've been able to change it as long as I
don't try to send data out. When I send something out, everything locks
up and I must do a cold boot. This mystifies me, because everything that
I am doing seems to make sense. Here's my setbaud.asm:
MCNTR EQU 41H ;Modem control port
RESET EQU 01000000B ;Value for port reset
MINIT1 EQU 01111010B ;Value for 1 stop bit, even parity,
; 7 data bits, 16X baud rate
MINIT2 EQU 00010101B ;Value for Error reset, transmit
;enable, receive enable
ORG 100H
INITIALISE: MVI A,RESET ;Puts 8251 in instruction mode
OUT MCNTR ;
MVI A,MINIT1 ;sets up baud, etc.
OUT MCNTR ;
MVI A,MINIT2 ;Puts 8251 back in normal mode
OUT MCNTR
JMP 0
This is pretty self explanatory, I guess... and it SHOULD work, but
there must be something that I'm missing...
Let me know what you can come up with.
Thanks again,
Mike
ihnp4!pur-ee!mjsGRUPP@mit-mc.ARPA (Paul R. Grupp) (12/31/85)
[ I don't think the mailer will hack your return address, so here it goes to the list at large ] First of all I think you want 8 data bits not 7, and the usual 1 stop bit, 16X baud clock. Second, to RE-init the 8251 you first have to send a command to it to turn it off, THEN the reset, init, and enable sequence. For 8 data, 1 stop, 16X here are the values in HEX. 0AAh 040h 0CEh 017h. Also you *CAN* change the baud rate (within limits) by changing the 1X, 16X, 64X clock devider rate. i.e. if you set the hardware switch to 1200 baud then by changing the 16X to 64X you would get 300 baud! Hope this helps. --Paul
jp@lanl.ARPA (12/31/85)
It's been a while, but I recall that the 8251 had a problem with reset. The solutions I've seen are 1: send reset several (3?) times, 2: go through the reset-program sequence twice. Don't know exactly what the problem with the 8251 is but that seems to fix it. AH, I found some code from my HAL MCEM-8080 (ca 1976). UARTI EQU 8EH ;INITIAL UART MODE WORD URTMO EQU 0EAH ;7 BITS, EVEN PARITY, 2 STOP URTCT EQU 0BH ;UART CONTROL PORT URTDA EQU 0AH ;UART DATA PORT UARTR EQU 55H ;RESET COMMAND TXRXE EQU 27H ;UART RX AND TX ENABLE INIT: MVI A,UARTI ;UART MODE OUT OUT URTCT MVI A,UARTR ;RESET OUT URTCT MVI A,URTMO ;FINAL UART MODE OUT URTCT MVI A,TXRXE ;ENABLE UART OUT URTCT RET The above code works. I have seen a slightly different way, but can't lay my hands on it this morning. I remember now that the 8251 comes on with its brains slightly scrambled. There are two control bytes that are sent to the same address sequentially and it doesn't know where it is in that sequence when first initialized. Hope this is some help. Jim Potter jp@lanl.arpa
brad@DCA-EUR.ARPA (01/02/86)
It has been 8 years since I worked on the BIOS for my NorthStar Horizon. I just dug out the code and found that you have to send the 8251 both a Mode Word to tell it either Async or Sync and a Command word. The code for my Horizon was: * Send Mode Word for Asynchronous Mode * MVI A,0CEH ; 2 Stops, 16XClock, 8 Bits, No Parity OUT 3 ; Send to 8251 (This different from Data Port) * Set up Control Word for 8251 * * RTS = Request To Send, ER = Error Reset * RXE = Receive Enable, DTR = Data Term Ready * TXEN = Transmit Enable * MVI A,37H ; CMD: RTS, ER, RXE, DTR, TXEN OUT 3 ; Output to 8251 Hope this helps. Brad
aep@abic.UUCP (Alex Pensky) (01/04/86)
> INITIALISE: MVI A,RESET ;Puts 8251 in instruction mode > OUT MCNTR ; > MVI A,MINIT1 ;sets up baud, etc. > OUT MCNTR ; > MVI A,MINIT2 ;Puts 8251 back in normal mode > OUT MCNTR > JMP 0 Hmm, how about that JMP 0? Does your BIOS reset the 8251 and write "reasonable" MINIT1 and MINIT2 bytes to it on a warm boot? Mine sure does (SANYO MBC-1000). I use a routine just like yours but I just return after calling it.