Vma301 (real time clock) user manual pin definition and primary power

Hello all,

Posting this entry to verify some properties of the Real Time Clock (RTC).

Downloaded the user manual from

  1. In this manual the pins are documented in the overview as:

    | Arduino  | VMA301 |
    | D5       | CE     |
    | D6       | I/O    |
    | D7       | SCLK   |
    | 5V       | VCC    |
    | GND      | GND    |

The pins on the hardware are indicated as:

Suggest to add these pinnames to the user manual.
Please confirm my values are correct!

| Arduino  | VMA301 | Pin names | 
| D5       | CE     | RST       |
| D6       | I/O    | DAT       |
| D7       | SCLK   | CLK       |
| 5V       | VCC    | VCC       |
| GND      | GND    | GND       |
  1. The primary power (VCC = VCC2) is indicated as 5V
    And in “Pin Layout” VCC is documented as
    “The VMA301 operates from the larger of VCC1 or VCC2.
    When VCC2 is greater than VCC1 + 0.2V, VCC2 powers the VMA301.”
    I read this as VCC2 can also be by 3.3V as the battery (VCC1) is rated 3V.
    Can you confirm this?

Thank you and kind regards,

Dear Bert,

I confirm your pin names are correct.

The pin names of manual come from the datasheet of DS1302 chip.
In datasheet is mentioned that CE is RST.

" Input. CE signal must be asserted high during a read or a write. This pin has an internal 40kΩ (typ) pulldown resistor to ground. Note: Previous data sheet revisions referred to CE as RST. The functionality of the pin has not changed." page 4 datasheet.

SLK is same as CLK (clock)

DAT = Data => is same as I/O

Second question:

You can power the VMA301 with 3V3 (3,3V) power.
In datasheet is mentioined that the typical voltage as power supply for DS1302 (VMA301) is 3,3V to max 5V. The absolute min voltage is 2V.

Velleman Support

1 Like

Hello @VEL450,

Thank you for your quick and extended answers.
All clear now :wink:

Kind regards,