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Page 2: ...Tynemouth MINI PET 40 80 2 www tynemouthsoftware co uk V1 82...
Page 3: ...rked 9X 1 103 pin 1 marked by dots on package and PCB SEMICONDUCTORS NEW TEXAS INSTRUMENTS ICS RECOMMENDED 3 x 1N4148 diodes no part number marked on the PCB 1 x 1N4001N diode marked on the PCB as 1N4...
Page 4: ...ini PET No PET ROM RAM PET Diagnostics 64K RAM boards or Super PET boards or anything not specifically designed for the Mini PET will work in that socket The chips that act as external driver chips th...
Page 5: ...Tynemouth MINI PET 40 80 5 www tynemouthsoftware co uk V1 82 PCB LAYOUT...
Page 6: ...ied as an upgrade to 2001N and 30xx machines and also on the 40xx machines It has additional disk commands over BASIC 2 and came in 40 or 80 column versions MINI PET BASIC 4 1 Mini PET BASIC is a cust...
Page 7: ...in 40 column mode and the 40 80 button on the keyboard can be used to change mode Changing mode also changes the ROM selection and resets the Mini PET DIP switch 5 controls the mode that is selected...
Page 8: ...bottom of the screen keeps count of the number of cycles and any errors detected RESET BUTTON The Mini PET reset button controls the video microcontroller When reset this provides a clean reset pulse...
Page 9: ...o activate those versions type SYS 59648 COMMANDS filename load the program filename filename load and run the program filename Display drive status at power on this will show drive version informatio...
Page 10: ...roll up or down one page of files Return load the select program change into the selected directory or mount the selected disk image Clr Home Move up one directory out of a disk image S Toggle sorting...
Page 11: ...hex digits e g 0094 78 D4 00 0D 00 D3 01 FF Any errors will either do nothing or a will appear in the line you have typed to indicate the error COMMANDS M start display 8 bytes of memory from this ad...
Page 12: ...count within the Mini PET reduces the loading on the address and data bus pins so they are no longer necessary RAM AND ROM The Mini PET has the full 32K of RAM a PET can support without paging This is...
Page 13: ...changes between 40 and 80 column mode Address Range 40 Column Mode 80 Column Mode Function 0000 7FFF 32K Main RAM 8000 83FF 1K 2K Video RAM 8400 8FFF 3K 2K Mirror of video RAM 9000 AFFF 8K Options ROM...
Page 14: ...e achieved a speed increase by changing the input on the VIA chip to an output and driving that signal low so it would appear it was always safe to draw the screen at the expense of visible snow This...
Page 15: ...ed using a resistor divider and open collector buffer On the Mini PET all the pins have been implemented using the second option as the original driver chips are no longer in production Board space is...
Page 16: ...Zener circuit would draw more power The output here will be about 6 2V The control transistor was replaced by a 7406 open collector buffer This would do nothing when Control is low and will short out...
Page 17: ...ARD The final IO chip is another W65C21N as PIA 2 This is mainly involved with the keyboard but also provides the remaining datasette and IEEE 488 signals The keyboard is a 10x8 matrix the rows drive...
Page 18: ...of the second inverter will be 9V The diode stops this being passed on and the NMI pin is pulled to 5V via one of the pullup resistors in the resistor array by the CPU When the NMI button is pressed t...
Page 19: ...utput is high the signal being pulled high by the 10K resistor This signal is optionally inverted again by the 74HC86 XOR gate depending on a DIP switch setting This allows the Mini PET to start in 80...
Page 20: ...gulators and a power LED a total of around 2mA mainly the LED Everything else is powered from 5V which is switched on or off as required There are two MIC2951 regulators used to supply the 5V rails Th...
Page 21: ...isolated and operate separately The video circuit on an original PET will show a screen full of random characters even if the CPU is removed or there is some fault which prevents it running code that...
Page 22: ...ss bus latching and buffering video data from both sides In the Mini PET those parts are all replaced by a single dual port video RAM chip The remaining parts divide down the main clock to generate al...
Page 23: ...ctor can provide green on black or white on black depending on the option selected via DIP switch 10 When the line and frame rates are within range a composite video signal is also generated The timin...
Page 24: ...re detailed in a separate section but in brief Switches 1 and 2 select the system ROM Switches 3 and 4 select the character font ROM Switch 5 selects if the Mini PET should start in 40 or 80 column mo...
Page 25: ...t has negative video and negative active low vertical sync but positive active high horizontal sync which ends part way into the visible line Later CRTCs PETs with 12 monitors changed the line frequen...
Page 26: ...SER PORT The user port provides general user IO functionality video and datasette signals There is a full 8 bit parallel IO port driven from the 6522 VIA This is not compatible with VIC20 or C64 userp...
Page 27: ...itor The pinout is the same for both 9 and 12 monitors but the signal polarity is different This is automatically set when selecting 9 or 12 monitor on the video DIP switches which also sets the appro...
Page 28: ...h 10 In White on Black mode the video is sent to Red Green Blue and Intensity inputs giving a bright white character In Green on Black mode 0V is sent to Red and Blue giving a bright green character P...
