RF60 Datasheet, PDF (114/157 Pages) –

RF60 CRYSTAL-LESS SOC TRANSMITTER v1.0
29.2. Pullup Roff Option
There is an option to disable the weak pullup pad resistors. This feature is called Roff option. The Roff
option is controlled directly by the GPIO pads and persist when the chip is in the shutdown mode. Control
of the Roff control bit in the GPIO is described in section 29.4. Pullup Roff and Matrix Mode Option Con-
trol.
29.3. Matrix Mode Option
The target application of the device is the button intensive application, which samples button pushes at the
device inputs and acts accordingly.
Given the pin limited package the target user application could use at most 5 buttons on 10 pin package
and 9 buttons on 14 pin package. If the chip is in a shutdown mode, any button push (connection to any
GPIO to ground) wakes the chip up.
For the applications requiring more push button inputs than there are available GPIO inputs, Matrix button
mode was implemented on the device. This allows the buttons to be organized in 3x2 matrix for 10 pin
package or 3x6 matrix for the 14 pin package allowing for up to 6 push buttons for 10 pin package and up
to 18 buttons on the 14 pin package. It is up to the firmware to scan the matrix sequentially to determine
the status of the buttons.
When the buttons are organized in Matrix mode any button push must wake the chip up from a shutdown
mode. Since the buttons are not connecting GPIO to ground, but connecting an input GPIO to some output
GPIO, the output GPIO must be connected to ground during the chip shutdown. That is achieved by setting
the Matrix option control bit in the GPIO latch. When that bit is set then the GPIO[3:1] are actively pulled to
ground when the chip is in the shutdown mode and digital logic has no power internally.
Note that to use the Matrix mode the Roff option must not be used. In other words, all the pullup resistors
must stay in place for all the GPIO. There should be values PORT_MATRIX=1 and PORT_ROFF=0
latched into GPIO options control latch.
When the Matrix mode is latched into the GPIO control latch the pullup resistors of the GPIO[3:1] are dis-
connected and the pull down transistor on those GPIOs is activated.
Important: Before invoking a Matrix mode the user is responsible for programming all GPIO[3:1] as
inputs. This is achieved by writing 1 to P0[3:1] and writing 0 to P0CON[3:1]. Only after that the Matrix
option can be invoked.
If the chip went to shutdown with Matrix option set, then it will be woken up by any button press of the but-
ton matrix. It is a responsibility of the user application which must turn the Matrix mode off before the soft-
ware can scan the button matrix for current button status. The button scanning is usually done scanning
the matrix driver pins GPIO[3:1] with one-cold pattern, applying sequential binary patterns GPIO[3:1]=110,
101, 011, and 111 using open drain configuration of the GPIO[3:1]. By collecting corresponding responses
on the GPIO[4,0] or GPIO[4,0,9:6], input GPIOs to the driving one-cold patterns firmware can determine
what buttons are currently pushed.
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