Lately I have been working on a universal ZBASIC programmer + rapid prototyping device (with a ZX-328L in it) and I am proud to present my results here as it proved extremely flexible and helpful. It is based on a circuit that allows any ZBASIC device to be programmed (the ZX24 and ZX40/ZX328 types are different in that the serial signals for programming are / are not inverted; this circuit allows programming them directly using separate connectors without having to change polarity settings in the FDTI chip). Furthermore, the circuit also has a barebones ZX328L circuit included to allow rapid development and testing of programs. The latter circuit can also be physically disconnected from the programming circuit if needed so as to act as a stand-alone controller as well, using simple connectors to attach the wiring. A switch is included to allow both 3.3V and 5V opoeration.
The circuit is contained in an old Iphone box, with guidelines printed on the back so as to help with connecting the device to an actual circuit. I hope the information presented here may inspire others to develop a simple programmer and prototyping circuit as well. Detailed information on settings is available in the circuit diagram picture, and I am happy to help with any remaining questions.
Some particular details:
- When used as a programmer, the relevant pins of the to be programmed ZBASIC device can be connected directly to the programming connector, no extra pullup-resistors are necessary as the necessary ones are already present on the programmer.
The inverter (74HC04) needs to be of this special type as it needs to be able to operate at both 3.3V and 5V. A 74CHT04 or 74LS04 will therefore not work.
The USB to TTL Serial device has been used, but any other device with similar characteristics may be applied as well. The settings need to be such that the 5V voltage is provided by the USB connection, and the voltage levels of the serial signals need to be at 3.3V. This is also indicated in the circuit diagram.
The programming circuit is equivalent with the one presented in the ZBASIC manual. The S2 slide switch is used to choose the operating voltage of the circuit.
The FDTI chip should be configured at installation such that the output signals DTR, RxD and TxD are inverted by default, as needed by the ZX24 type. The ZX40 and ZX328 types expect non-inverted signals, therefore the 74HC04 inverter is used.
The LED is used to signal 3.3V as the selected main voltage. A red, diffusive type needs to be used since only those have a low enough forward voltage drop to allow it to be used as shown in the circuit diagram.
Jurjen