Add README for variants

Author: Senbei64

README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ![blink board](img/blink_board.jpg)
 
@@ -23,11 +23,11 @@ void loop(void)
 
 ### Commodore User Port
 
-|  1  |  2  |  3  |  4  |  5  |  6  |  7  |  8  |  9  |  10 |  11 |  12 |
-|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|:---:|
-| GND |_(1)_|_(1)_|_(1)_|_(1)_|_(1)_|_(1)_|_(1)_|_(1)_|_(1)_|_(1)_| GND |
-| GND |_(2)_|I/O 0|I/O 1|I/O 2|I/O 3|I/O 4|I/O 5|I/O 6|I/O 7|_(2)_| GND |
-|**A**|**B**|**C**|**D**|**E**|**F**|**H**|**J**|**K**|**L**|**M**|**N**|
+|  PIN_1  |  PIN_2  |  PIN_3  |  PIN_4  |  PIN_5  |  PIN_6  |  PIN_7  |  PIN_8  |  PIN_9  |  PIN_10 |  PIN_11 |  PIN_12 |
+|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|
+|   GND   |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |   GND   |
+|   GND   |  _(2)_  |  I/O 0  |  I/O 1  |  I/O 2  |  I/O 3  |  I/O 4  |  I/O 5  |  I/O 6  |  I/O 7  |  _(2)_  |   GND   |
+|**PIN_A**|**PIN_B**|**PIN_C**|**PIN_D**|**PIN_E**|**PIN_F**|**PIN_H**|**PIN_J**|**PIN_K**|**PIN_L**|**PIN_M**|**PIN_N**|
 
 _(1)_ Pins of the upper row differ significantly between systems.
 Some of them can be used as additional input or output lines.

alternatives/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Alternatives
 This directory contains examples written without the **blink65** library.

alternatives/blinkbasic64/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Blink - BASIC
 This exapmple is written without the **blink65** library.

examples/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Examples
 This directory contains examples written with the **blink65** library.

examples/blink/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Blink
 The classic blink example.

examples/simple64/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Simple 64
 This example uses the same sketch as the blink example,

examples/tones/README.md

@@ -1,5 +1,5 @@
 # blink65
-Write Arduino-style sketches for VIC-20 and Commodore 64.
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
 
 ## Tones
 Using the tone() function.

library/c64/README.md

@@ -0,0 +1,20 @@
+# blink65
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
+
+### Commodore 64 User Port
+
+|  PIN_1  |  PIN_2  |  PIN_3  |  PIN_4  |  PIN_5  |  PIN_6  |  PIN_7  |  PIN_8  |  PIN_9  |  PIN_10 |  PIN_11 |  PIN_12 |
+|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|
+|   GND   |  +5V DC |  /RST   |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  |  _(1)_  | 9V AC + | 9V AC - |   GND   |
+|   GND   |  _(1)_  |   PB0   |   PB1   |   PB2   |   PB3   |   PB4   |   PB5   |   PB6   |   PB7   |   PA2   |   GND   |
+|**PIN_A**|**PIN_B**|**PIN_C**|**PIN_D**|**PIN_E**|**PIN_F**|**PIN_H**|**PIN_J**|**PIN_K**|**PIN_L**|**PIN_M**|**PIN_N**|
+
+_(1)_ Pins available via direct programming of CIA chips.
+
+### Commodore 64 Variant
+The ```tone()``` function uses Timers A and B in free-run mode to toggle pins PB6 (**PIN_K**) and PB7 (**PIN_L**) of CIA 2,
+respectively, at the required frequency.
+
+The supported frequency range is between 10 Hz and 65 kHz.
+
+Pins must be explicitly set to output mode.

library/pet/README.md

@@ -0,0 +1,21 @@
+# blink65
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
+
+### Commodore PET User Port
+
+|  PIN_1  |  PIN_2  |  PIN_3  |  PIN_4  |  PIN_5  |  PIN_6  |  PIN_7  |  PIN_8  |  PIN_9  |  PIN_10 |  PIN_11 |  PIN_12 |
+|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|
+|   GND   |  _(1)_  |  _(2)_  |  _(2)_  |  _(2)_  |  _(2)_  |  _(2)_  |  _(2)_  |  _(1)_  |  _(1)_  |   GND   |   GND   |
+|   GND   |  _(2)_  |   PA0   |   PA1   |   PA2   |   PA3   |   PA4   |   PA5   |   PA6   |   PA7   |   CB2   |   GND   |
+|**PIN_A**|**PIN_B**|**PIN_C**|**PIN_D**|**PIN_E**|**PIN_F**|**PIN_H**|**PIN_J**|**PIN_K**|**PIN_L**|**PIN_M**|**PIN_N**|
+
+_(1)_ Pins used for the video signal.
+_(2)_ Pins available via direct programming of PIA and CIA chips.
+
+### Commodore PET Variant
+The ```tone()``` function uses the VIA Shift Register in free-run mode,
+combining the Timer 2 rate with specific Shift Register patterns to output the required frequency on pin CB2 (**PIN_M**).
+
+The supported frequency range with this method is between 243 Hz and 65 kHz.
+
+Pin is implicitly set to output mode.

library/vic20/README.md

@@ -0,0 +1,26 @@
+# blink65
+Write Arduino-style sketches with cc65 for VIC-20, PET, and Commodore 64.
+
+### Commodore VIC-20 User Port
+
+|  PIN_1  |  PIN_2  |  PIN_3  |  PIN_4  |  PIN_5  |  PIN_6  |  PIN_7  |  PIN_8  |  PIN_9  |  PIN_10 |  PIN_11 |  PIN_12 |
+|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|:-------:|
+|   GND   |  +5V DC |  /RST   |   PA2   |   PA3   |   PA4   |   PA5   |   PA6   |   PA7   | 9V AC + | 9V AC - |   GND   |
+|   GND   |  _(1)_  |   PB0   |   PB1   |   PB2   |   PB3   |   PB4   |   PB5   |   PB6   |   PB7   |   CB2   |   GND   |
+|**PIN_A**|**PIN_B**|**PIN_C**|**PIN_D**|**PIN_E**|**PIN_F**|**PIN_H**|**PIN_J**|**PIN_K**|**PIN_L**|**PIN_M**|**PIN_N**|
+
+_(1)_ Pins available via direct programming of VIA chips.
+
+### Commodore VIC-20 Variant
+The ```tone()``` function supports two different output methods depending on the pin:
+- PB7 (**PIN_L**): Uses Timer 1 of the 6522 VIA in free-run mode to toggle the pin.
+  
+  This 16-bit timer allows a very wide frequency range, clamped between 10 Hz and 65 kHz in this implementation.
+
+  The pin must be explicitly set to output mode.
+- CB2 (**PIN_M**): uses the VIA Shift Register in free-run mode,
+  combining the Timer 2 rate with specific Shift Register patterns to output the required frequency.
+
+  The supported frequency range with this method is between 271 Hz and 65 kHz, on PAL systems, and between 248 Hz and 65 KHz on NTSC systems.
+
+  Using this method, PIN_M is implicitly set to output mode, as is PIN_B, where Timer 2 clock is emitted.