Power, Reset, and Mode Selection Lines




Positive power input, 5V nominal, +/- 5%, app. 50mA












Reset, active high




Mode selection pin

Line functions defined by the application firmware are shown in blue

The EM120 should be powered from a stabilized DS power supply with output nominal voltage of 5V (+/- 5% tolerance). Current consumption of the EM120 is approximately 50mA.

Proper external reset is a must! Reset pulse should be an active HIGH. We strongly advise against using low-cost RC-networks and other unreliable methods of generating reset pulse. Reset should be applied for as long as the power supply voltage is below 4.6V. We recommend using a dedicated reset IC with brownout detection, such as MAX810. Reset pulse length should be no less than 50ms, counting from the moment the power supply voltage exceeds 4.6V.

If the EM120 is used to serve as a communications co-processor in a larger system that has its own CPU it is also OK to control the RST line of the EM120 through a general-purpose I/O pin of the "host" microcontroller. I/O pins of many microcontrollers default to HIGH after the powerup and this means that the reset will be applied to the EM120 at the same time when the host microcontroller is reset. All the host microcontroller has to do is release the EM120 from reset at an appropriate time by switching the state of the I/O line to LOW.

The MD line of the EM120 is used to select the operating mode of the EM120 and/or its application firmware. The reason why the pin name is shown as MD(MD) is because the functionality of this pin is in part hardwired and in part depends on the application firmware :

Hardwired functionality. When the EM120 powers up it verifies the state of the MD input. If the MD input is at HIGH the EM120 proceeds to verifying and running the application firmware loaded into its internal FLASH memory. If the MD input is at LOW the EM120 enters the serial upgrade mode. For more information see Monitor.
Application firmware-dependent functionality. When the application firmware is already running the MD line is typically used to make the EM120 enter the serial programming mode. For more information see serial programming.

When the EM120 is used as a co-processor in a host system the MD line can be also controlled by the host microcontroller. Ability to control both the RST and DS lines allows the host microcontroller to switch between the operating modes of the EM120.