PT7C4363_13 Datasheet, PDF (15/20 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4363
Real-time Clock Module (I²C Bus)
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Operation example:
1. Set EXT_CLK test mode (control/status 1, bit TEST1 = 1)
2. Set STOP (control/status 1, bit STOP = 1)
3. Clear STOP (control/status 1, bit STOP = 0)
4. Set time registers to desired value
5. Apply 32 clock pulses to SQW
6. Read time registers to see the first change
7. Apply 64 clock pulses to SQW
8. Read time registers to see the second change.
Repeat 7 and 8 for additional increments.
2. Power-On Reset (POR) override
The POR duration is directly related to the crystal oscillator start-up time. Due to the long start-up times experienced by these
types of circuits, a mechanism has been built in to disable the POR and hence speed up on-board test of the device. The setting of
this mode requires that the I²C-bus pins, SDA and SCL, be toggled in a specific order as shown in Fig 6.4.2. All timings are
required minimums.
Once the override mode has been entered, the device immediately stops being reset and normal operation may commence i.e.
entry into the EXT_CLK test mode via I²C-bus access.
The override mode may be cleared by writing a logic 0 to TESTC. TESTC must be set to logic 1 before re-entry into the override
mode is possible. Setting TESTC to logic 0 during normal operation has no effect except to prevent from entering the POR
override mode.
Power up
Fig.3 POR override sequence
Override active
Communication
1. I²C Bus Interface
a) Overview of I²C-BUS
The I²C bus supports bi-directional communications via two signal lines: the SDA (data) line and SCL (clock) line. A combination
of these two signals is used to transmit and receive communication start/stop signals, data signals, acknowledge signals, and so on.
Both the SCL and SDA signals are held at high level whenever communications are not being performed. The starting and
stopping of communications is controlled at the rising edge or falling edge of SDA while SCL is at high level. During data
transfers, data changes that occur on the SDA line are performed while the SCL line is at low level, and on the receiving side the
data is captured while the SCL line is at high level. In either case, the data is transferred via the SCL line at a rate of one bit per
clock pulse. The I²C bus device does not include a chip select pin such as is found in ordinary logic devices. Instead of using a
chip select pin, slave addresses are allocated to each device and the receiving device responds to communications only when its
slave address matches the slave address in the received data.
b) System Configuration
All ports connected to the I²C bus must be either open drain or open collector ports in order to enable AND connections to
multiple devices.
SCL and SDA are both connected to the VDD line via a pull-up resistance. Consequently, SCL and SDA are both held at high
level when the bus is released (when communication is not being performed).
2013-06-0002
PT0207-6 06/18/13
15