The Osborne I's uart is memory mapped in bank 2 at locations
02A00H and 02A01H. The traditional way of getting at the port
was to have some assembly language code located above 04000H.
This code normally takes the form of:
DI
OUT 00H
To change back you have used the following:
OUT 01H
EI
The uart is mapped with 02A00H as the status/control word and
02A01H as the data word. So to write some data to the data port
of the uart, the following code would have been used:
DI
OUT 00H
STA 02A01H
OUT 01H
EI
This is the new method that uses code that is already in the BIOS
and the ROM. What you have to do is set up somthing like the
following code:
;Output a control word to the 6850 chip
CTLPOUT:
MOV C,A ;Put the character in C
LXI D,013CH
JMP SWITCH
;Input the status of the 6850 chip
STATUS: LXI D,0181H
CALL SWITCH
RET ;The status will be in A
;Output a charater to the 232 port
DTLPOUT:
MOV C,A ;Put the charater in C
LXI D,010FH
JMP SWITCH
;Input a character from the 232 port
DTLPIN: LXI D,0115H
CALL SWITCH
RET ;The character will be in A
SWITCH: LDA SWITCH1+2
ORA A
RZ ;Nont installed yet
SWITCH1:
JMP 0036H ;The 00 is replaced by INIT
;END OF CODE
The code should be installed with the following code:
INIT: LDA 0002H ;High order bit of the BIOS addr
STA SWITCH1+2
RET
;END OF CODE
When using this method of getting to the 6850 chip, you should
always call the STATUS routine before calling DTLPIN because
DTLPIN will wait for a character and if there is no character for
a while, the program will be locked up. The code that is used to
mask off and check the status bits is still the best way of
checking for Ready-for-the-next-character and Character-is-
waiting.
The data words are the usual ascii characters. The data for the
control word is in the first chart. The status word definitions
are in the second chart.
In the following charts, CR0 is the least significant bit and CR7
is the most significant bit.
CR7 FUNCTION
X Is not used on the Osborne.
CR6 CR5 FUNCTION
0 0 Enables the internal modem port on the Osborne.
0 1 Not used on the Osborne.
1 0 This is the normal setting.
1 1 Transmits a BREAK level on the data output.
CR4 CR3 CR2 FUNCTION
0 0 0 7 Bits, Even parity, 2 Stop bits
0 0 1 7 Bits, Odd parity, 2 Stop bits
0 1 0 7 Bits, Even parity, 1 Stop bit
0 1 1 7 Bits, Odd parity, 1 Stop bit
1 0 0 8 Bits, No parity, 2 Stop bits
1 0 1 8 Bits, No parity, 1 Stop bit
1 1 0 8 Bits, Even parity, 1 Stop bit
1 1 1 8 Bits, Odd parity, 1 Stop bit
A Master Reset (03H) must be written to the uart before a new
setting is sent and as the first thing written to the uart after
the program starts. The 19,200 baud setting does not seem to
work on the Osborne I.
CR0
0 Data not available
1 Data available
CR1
0 Not ready for new data
1 Ready for new data
CR2
0 Carrier present
1 Carrier lost
CR3
0 Clear to send (hooked to the CTS line)
1 Not clear to send
CR4
0 No framing error
1 Framing error
CR5
0 No overrun error
1 Overrun error
CR6
0 No parity error
1 Parity error
CR7
X Not used on the Osborne I
I hope that this code modification will make it easier for you to
install a term program on your system.
he Osborne I
I hope that this code modification will make it easier for you to
install a term program on
