Simple digital clock, displays hours, minutes, and seconds in either a 24h format.
Since there are not enough output pins to directly drive a 6x
7-segment displays, the data is shifted out serially using an internal 8-bit shift register.
The shift register drives 6-external 74xx596 shift registers to the displays. Clock and control
signals (serial_clk, serial_latch) are also used to shift and latch the data into the external
shift registers respectively. The time can be set using the hours_set and minutes_set inputs.
If set_fast is high, then the the hours or minutes will be incremented at a rate of 5Hz,
otherwise it will be set at a rate of 2Hz. Note that when setting either the minutes, rolling-over
will not affect the hours setting. If both hours_set and minutes_set are presssed at the same time
the seconds will be cleared to zero.
Connect serial output to a 6x 8-bit shift registers to display the output on 6x 7-segment displays
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | refclk | serial_data | none |
| 1 | use_refclk | serial_latch | none |
| 2 | fast_set | serial_clk | none |
| 3 | hours_set | none | none |
| 4 | minutes_set | none | none |
| 5 | none | none | none |
| 6 | none | none | none |
| 7 | none | none | none |