Serial interface specification/Keypad interface specification

Voltage/Signal level Serial Interface/Keypad for different camera generations

The serial interface hardware has changed from the early VCxx to the current range VC4xxx model - so has the keypad interface. For this reason, different keypads are required for each camera series.

This article includes the power supply and signal level specifications of all keypad interfaces.

The RS232C norm specifies a signal level range from +-3V to 12V. In general, Voltage level have dropped over the years, with most modern RS232 interfaces just supplying LVTTL levels around 3.3V.

These changes also reflect the technical development of the V24 (RS232) of VC cameras. 3rd party equipment needs to match the requirements of each camera generation. Even within one series there may be subtle differences in signal levels - however all true serial interfaces meet the RS232 norm.

General changes to the keypad interface/RS232 Interface:

• The VCxx Keypad was attached to the serial V24 camera interface and therefore used a nominal supply voltage of +-12V (+- 25%). Refer to the keypad manual attached.
• The VC20xx and VC4xxx Keypads are attached to the trigger interface and use the GND/5V supply from this interface.
• In contrast to the VC20xx, the VC4xxx has a true bi-directional RS232 interface (+-3,3V). The VC20xx trigger interface only had a "Keypad In" line (signal level 0-5V). Note the new trigger input circuit required for VC4xxx cameras resulting from this modification! (Refer to VC4xxx HW manual for details.)
• The chips used are: VC20xx-MAX202, VC4xxx-MAX3223 (from S/N XX1XXXX), the C4 keypad for VC4xxx cameras uses a MAX3227 chip (see linked downloads to this article). Data sheets can be downloaded from http://www.maxim-ic.com/.
• The signal levels may vary slightly within a camera series, however all chips used comply with the RS232C norm.