Canon Functions - Metz mecablitz 44 MZ-2 Servicehandbuch

Technik und Service Seite: 43
Technology and Service Page: 43
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
7. Canon Functions (mecablitz 44 AF-3C):
Camera interface:
On the mecablitz 44AF-3C, the interface to the camera consists of six contacts: SYN
contact, special contacts SK1 to SK4 and two ground contacts on the sides
(connected in parallel).
(Contacts, viewed from below)
Data are exchanged between the mecablitz and the camera on three wires. On these lines, the LOW level is
about 2.2 V instead of the more usual 0 V.
Processing and evaluation of the camera data:
The mecablitz receives the camera data via special contact SK3. The incoming signal drives the base of Tr409
via the RC circuit R4035/C408 and resistor R4036. Since the LOW level of this signal is about 2.2 V, it is
necessary to ensure that Tr409 does not conduct with the LOW level applied. For this purpose, the emitter of
Tr409 receives a stable bias voltage of about 2 V from R4041 and Zener diode D407, which are connected in
series. This bias voltage ensures that Tr409 conducts only when a voltage of more than 2.7 V (i.e. the HIGH
level) is present. Since the following digital circuits and the µC IC401 can process only 0 V as the LOW level,
the input signal must be converted accordingly. This is done by the comparator IC403A in the collector circuit
of Tr409.
The CLOCK signal from the camera (on special contact SK4) is needed so that the µC of the mecablitz can
process the camera data. Since the CLOCK signal also has a LOW level of about 2.2 V, special processing is
again necessary, and this is done by IC403B, which acts as a comparator.
The Zener diode D412 limits the input voltage at SK4 if an incorrect device (such as a camera which does not
belong to the Canon camera system) is connected to this contact. R4056 limits the current through the Zener
diode.
Processing and output of the flash data:
Due to the system design, the outgoing flash data (on special contact SK1) must also be processed so that the
camera can evaluate them correctly. The LOW level of the flash data must be raised to about 2 V to 2.2 V.
This is done with IC404 and the circuits after this IC.
Transmission of the "flash ready" signal and activation of the AF measuring beam:
With the measuring system of the camera active, there is a voltage of about 1.2 V on contact SK2. When the
mecablitz is ready for firing, the µC IC401 switches pin 33 (BB_OUT) to HIGH. Tr408 therefore conducts and
draws a current of about 0.3 mA from the camera via R4030 and SK2. This indicates to the camera that the
mecablitz is ready for firing.