Pentax Functions - Metz mecablitz 44 MZ-2 Servicehandbuch

Technik und Service Seite: 50
Technology and Service Page: 50
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
10. Pentax Functions (mecablitz 44 AF-3P):
Camera interface:
On the mecablitz 44 AF-3P, the interface to the camera consists of five contacts:
SYN contact, special contacts SK1, SK2 and SK3, ground contact.
(Contacts on the mecablitz, viewed from the bottom)
Data bus:
Data are exchanged between the mecablitz and the camera on two lines. SK1 is the common data line, on
which camera and flashgun data are transmitted alternately, whereby the camera and flashgun have distinctly
different HIGH levels. SK2 carries the CLOCK signal from the camera to the flashgun. SK3 is used to
coordinate the data transfer: with this contact, the camera determines whether the flashgun is to transmit or
receive data.
Data output from the mecablitz:
The CLOCK signal of the camera on SK2 has a HIGH level of about 4.1 V. It is inverted by transistor Tr408.
The inverted CLOCK signal at the collector of Tr408 passes to Pin 36 (CLK) of the µC IC401. The µC IC401
generates the flash data at Pin 31 (DATA_OUT). For system-design reasons, it is necessary to reduce the HIGH
level of the flash data to about 1.4 V at SK1. For this, the base of Tr409 is driven via the voltage divider
consisting of R4034 and R4035, which results in a voltage of about 2.0 V at the base of Tr409. The base-
emitter threshold voltage of Tr409 is subtracted from this, resulting in a HIGH level of about 1.4 V at SK1.
Reading data from the camera:
In order to read data from the camera, Tr409 must be cut off. To do this, Pin 31 (DATA_OUT) of the µC
IC401 is switched to LOW. The data signal arriving from the camera on SK1 drives the base of Tr410 via
R4036 and R4038 and is then available as an inverted signal at the collector of Tr410 and at Pin 32
(DATA_IN) of µC IC401, where it is evaluated.
Synchronisation:
In order to trigger a flash, the camera connects the SYN contact to ground. For synchronisation with the first
curtain, the camera leaves contact SK1 at LOW level before the SYN time (when SYN switches from HIGH to
LOW).
For Pentax cameras, synchronisation with the second curtain (REAR) can be selected on the mecablitz. In this
case, the signal sequence on SK1 is different: the flash is triggered only when SK1 changes from HIGH to
LOW after the SYN time.