keypad_emu_arch Architecture Reference

Architecture is based on multiple concurrent assignments to the same signal, but some of the drivers are weak (pullups), just like the real hardware. More...

Detailed Description

Architecture is based on multiple concurrent assignments to the same signal, but some of the drivers are weak (pullups), just like the real hardware.

Each pressed key connects a row to a column, so we have a second driver for rows here. If multiple keys are pressed, we may have multiple strong drivers with different values for the same column, depending on what values the user puts in the rows, which could result in an 'X' in simulation. In the hardware, the internal resistances avoid a short-circuit, but the resulting value is not defined.

The keys in the physical keyboard are:

	Col0	Col1	Col2	Col3
Row0	1	2	3	A
Row1	4	5	6	B
Row2	7	8	9	C
Row3	0	F	E	D

(Please note that Digilent's schematics are slightly outdated and do not reflect the actual key layout. The correct key layout is in the table above)

The correspondence, for this simulation model, between the keys and the bits in the pressed_keys input is:

pressed_keys(i) to Row/Col/Key

i	Row	Col	Key
0	0	0	1
1	0	1	2
2	0	2	3
3	0	3	A
4	1	0	4
5	1	1	5
6	1	2	6
7	1	3	B
8	2	0	7
9	2	1	8
10	2	2	9
11	2	3	C
12	3	0	0
13	3	1	F
14	3	2	E
15	3	3	D

Definition at line 82 of file keypad_emu.vhd.

Processes
PROCESS_0	( pressed_keys , keypad_columns )

Constants
keypad_table	char_vector := ( ' 1 ' , ' 2 ' , ' 3 ' , ' A ' , ' 4 ' , ' 5 ' , ' 6 ' , ' B ' , ' 7 ' , ' 8 ' , ' 9 ' , ' C ' , ' 0 ' , ' F ' , ' E ' , ' D ' )

Types
char_vector	( 0 to 15 ) character

Signals
last_pressed_keys	std_logic_vector ( 15 downto 0 )

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The documentation for this class was generated from the following file:

• src/keypad_emu.vhd