DIY Southern Cross II Manuale hardware - Pagina 7
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Stampa la paginaThe signal " /IOEXP " is the block decode signal for the expansion interface and should be used in
conjunction with address lines A0-A7 to provide further address decoding.
Address lines A0-A7 have already been de-mulitplexed on the Southern Cross II board ie. they are actually
address lines. This allows devices with separate address and data lines to be connected to the expansion
interface directly. For those devices with a multiplexed address/data bus use signals AD0-AD7 and ALE.
An optional clock/calendar device is available for the Southern Cross II, a Dallas Semiconductor DS1216C
Intelligent Socket. Access to this clock/calendar is provided in the MVS-31 debugging monitor.
The DS1216C contains an internal lithium battery. This keeps the clock going during power down and also
makes the CMOS RAM non-volatile ie. no loss of data when power to the Southern Cross II is removed.
Battery life is over 10 years. No circuit modifications are necessary to use the DS1216C, just plug it in
between the RAM chip and the IC socket (or solder directly to the PCB if purchased with the Southern Cross
II kit).
As mentioned, the Southern Cross II board is capable of being programmed in BASIC. A number of
suppliers, such as Intel and Micromint Inc., have available an 8052 microcontroller with a BASIC interpreter
programmed into the chip's internal EPROM. The Southern Cross II needs one of these chips installed as IC1
in order run the BASIC-52 language.
BASIC-52 has the ability to store its programs into an external memory device such as EPROM.
Programming EPROMs requires a voltage level of between 12.5 and 25 volts ( depending on the EPROM ).
The Southern Cross II generates this programming voltage using a DC-DC converter chip, IC12.
The Southern Cross II is designed to use a 27256 EPROM for storing BASIC programs. These EPROMs
require a programming voltage of 12.5 volts. Before attempting to save any programs in EPROM, the
programming voltage must be set to this level. This is done by measuring the voltage on test pin TP1 and
adjusting trimpot VR1 for 12.5 volts. This procedure is only required once. However it is worth checking this
voltage periodically or whenever any problems occur with saving programs to EPROM.
The Southern Cross II only uses 27256 EPROMs for saving BASIC programs. Remove the MVS-31 monitor
EPROM and install a 27256 type in its place. The MVS-31 monitor can reside on the same 27256 EPROM
used to save BASIC programs. The monitor would reside in the bottom 8K starting at address 0000h whereas
BASIC programs are saved at address locations 8000h upwards, which is in the upper 16K of the EPROM.
The memory decoder GAL, IC9, splits the EPROM into two halves, with one half starting at 0000h and the
other half starting at 8000h. Remember to set jumper JP2 to the correct EPROM type. A number of BASIC-
52 programming and startup options are also available. Refer to the BASIC-52 reference manual for further
details.
BASIC-52 uses port bits P1.3, P1,4 and P1.5 as EPROM programming control lines. The function of these
lines is:
These signals are not connected directly to the EPROM or associated programming circuitry. Instead they are
connected via switch SW2 and the memory decoder GAL, IC9. When the GAL detects a low on its pin 5, it
uses these port bits to control the output signals " /ROM_CE, SYS_ALE and /VPP_CONT ". Moving SW2 to
the " ON " position connects the port bits to the GAL and pulls pin 5 low, ready for EPROM programming.
These port bits can also be used as general purpose I/O lines and are brought out on connector J1. These pins
MUST be isolated from any external voltage levels. This would be the case if any of these pins were inputs
Clock/Calendar
BASIC-52 Programming
P1.3
ALE Disable
P1.4
Program pulse width
P1.5
Enable program voltage