Minolta Functions - Metz mecablitz 44 MZ-2 Servicehandbuch

Technik und Service Seite: 45
Technology and Service Page: 45
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
The comparator IC403B which monitors the special contact SK4 is connected to the +5.0V supply voltage
(which remains on in standby mode). When the user touches the shutter release button the camera sends a
CLOCK signal to the mecablitz on SK4. This signal is detected by the comparator IC403B and sent to the
interrupt input at pin 51 (CLK/TTL) of the µC IC401. The µC then switches the mecablitz on again.
7. Minolta Functions (mecablitz 44 AF-3M):
Camera interface:
On the mecablitz 44 AF-3M, the interface to the camera consists of four contacts:
SYN contact, special contacts SK1 and SK2, 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. SK2 carries the CLOCK signal from the camera
to the flashgun.
Data output from the mecablitz:
The CLOCK signal of the camera on SK2 has a HIGH level of about 2.6 V. This is inverted twice in the
transistor stages Tr411 and Tr410 to convert the HIGH level of the CLOCK signal to 5 V. The CLOCK signal
at the collector of Tr410, which has the same phase as the incoming signal but a higher level, passes to the
CLK input (Pin 3) of the D-flip-flop (D-FF) in IC403.
Pin 31 (DATA_OUT) of µC IC401 generates a level corresponding to that of the data information arriving at
the D input of the D-FF in IC403. With the positive-going edge of the CLOCK signal, the level at the D input
(Pin 3) is transferred to the Q output (Pin 1) of the D-FF. Pin 2 of the D-FF carries a level which is the
complement of the level at Pin 1. This drives the base of Tr409 via R4034 and C408. This is inverted by
Tr409, whose collector generates the data output signal for the camera on SK1.
Reading data from the camera:
In order to read data from the camera, Tr409 must be cut off. To do this, the output at Pin 2 of the D-FF in
IC403 is held at a LOW level. This is done by µC IC401, which switches its output at Pin 36
(ENFORCED_HIGH) to HIGH level. This enforces a HIGH level at the D-FF output at Pin 1 and thus a LOW
level at the complementary D-FF output at Pin 2. This ensures that Tr409 is cut off. The data signal arriving
from the camera on SK1 drives the base of Tr408 via R4032 and is then available as an inverted signal at the
collector of Tr408 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. It is also necessary, amongst other
things, that the flashgun switches the contact SK1 briefly to LOW. For this purpose, Tr409 is turned on by a
HIGH level at Pin 2 of IC403 (NOT-output of the D-flip-flop).