Gizmo's Projects: CGKEYCHIP1 Custom Keypad Example

The Maximite design uses a PS/2 connection as a keyboard interface. You can use a full keyboard connected to either a CGCOLORMAX1 or the CGMMSTICK1.

If you want to embed either of these two setups into a project, you might choose to replace the full keyboard with something either more compact or custom for your application. The CGKEYCHIP1 wired into a “ColorMax” or “stick” lets you create your own keyboard by adding your own buttons.

The CGKEYCHIP1 is a 24 pin chip in a DIP (through-hole) package. Four wires connect to the Maximite that include ground, power, and the two PS/2 communication signals (data/clock). You can wire in twelve distinct buttons for the keyboard keys plus three “modifier” buttons.

The CGKEYCHIP1 has two sets of keys that it can transmit:

Set1	Set2
F1	Up Arrow
F2	Down Arrow
F3	Left Arrow
F4	Right Arrow
F5	Space Bar
F6	Page Up
F7	Page Down
F8	Enter
F9	End
F10	Home
F11	Tab
F12	Backspace

An input pin on the chip selects between these sets of keys.

The CGKEYCHIP1 runs off of the 5V that the PS/2 connection provides. Both chip grounds should be connected to ground. The pins marked “NoConnect” should not be connected to anything.

Supplied with the CGKEYCHIP1 is a 1.3 kohm resistor that has to be connected from pin 11 to pin 15 for the chip to operate correctly

The PS/2 data signals are open-collector signals. When you connect the GCKEYCHIP1 to a CGCOLORMAX1 there are pull up resistors already on the ColorMax. When you connect to a CGMMSTICK1 and CGVGAKBD1 combination, the CGVGAKBD1 board already has pull up resistors in place for the two PS/2 lines. No additional resistors are needed in this case.

When you connect the CGKEYCHIP1 to just a CGMMSTICK1, you will need to attach two pull-up resistors in order to have the chip function correctly. Each of the two PS/2 lines should be pulled to 5V through a 10 kohm resistor.

The SetSelect input to the CGKEYCHIP1 selects the key set that you wish to use, either set 1 or set 2. Connecting this input directly to 5V will select set 1, while connecting this input to ground selects set 2.

The key inputs are activated by momentary contact to ground. Simple SPST buttons can be used.

You can write a very simple MMBasic program to check the codes that the keys transmit against the list of codes found in this document:

a$ = inkey$

if a$ <> "" then

print asc(a$)

endif

loop

When run, set 1 will return these codes:

Key	Plain	Control	Shift	Shift+Control
F1	145	209	177	241
F2	146	210	178	242
F3	147	211	179	243
F4	148	212	180	244
F5	149	213	181	245
F6	150	214	182	246
F7	151	215	183	247
F8	152	216	184	248
F9	153	217	185	249
F10	154	218	186	250
F11	155	219	187	251
F12	156	220	188	252

Set 2 returns these codes :

Key	Plain	Control
Up Arrow	128	192
Down Arrow	129	193
Left Arrow	130	194
Right Arrow	131	195
Space Bar	32	0
Page Up	136	200
Page Down	137	201
Enter	13	13
End	135	199
Home	134	198
Tab	9	9
Backspace	8	8

MMBasic interprets the Alt as a key by itself, not a modifier. The keycode for the Alt key is 139, Control-Alt is 203, Shift-Alt is 171, Control-Shift-Alt is 235. This program will return two key codes when Alt is used, first the Alt code, then the key code. Control-Shift-Alt-F1, for example, returns 235 241.