External
Program
Memory
External
Data
Memory
0000h
EPROM
( MVS-31 )
RAM
0000h
2000h
EPROM
4000h
Common
program and
⇒
data space
RAM
OPTIONAL CLOCK/CALENDAR( See text )
7FFFh
8000h
EPROM
8000h
C000h
SPI
F000h
VACANT
PPI
F400h
I/O EXPANSION
F800h
BIT PORT 1
FC00h
BIT PORT 2
FD00h
BIT PORT 3
FE00h
BIT PORT 4
FF00h
Fig 1
Serial Ports
These are implemented as simple "3-wire" interfaces, using just TxD, RxD and GND. The modem control
lines "CTS, DSR and DCD" are held at the RS-232 "ON" level and do not provide any hardware
handshaking. No software handshaking protocol is used either.
The Southern Cross II has two serial ports.
1.
Uses the internal serial port of the 8032/52 chip and is referred to as the "USER" port. Connection is via
the 10-pin header labelled J6.
2.
Uses an external SC2691 UART chip from Philips Components and is referred to as the "HOST" port.
Connection is via the 10-pin header labelled J5
The RS-232 signals are brought out to standard D9 connectors by using a 10-way flat ribbon cable. One end
is terminated with a 10-pin IDC plug and the other end with a crimp-style female D9 connector. By
connecting pin 1 on the 10-pin plug with pin 1 on the D9 connectors, the signals will be in the correct
positions to allow a "straight-through" connection to a D9-type PC COM port.
RS-232 Interface - J5, J6
Signal
J5, J6 pin
D9 pin
TxD
3
2
RxD
5
3
CTS
6
8
DSR
2
6
GND
9
5
DCD
1
1
