Hardware interface

PM0064

4/13

Doc ID 16274 Rev 3

2.3

Voltage levels for communication

The following table gives the voltage specifications. It is recommended to use the typical

values when designing a programming tool.

Caution:

All I/Os must have the same voltage level as VREG.

During option programming, the supply voltage of the STM8T141 is raised to 6.7 V. It is

recommended to make sure that the I/Os of the programmer can operate at 6.7 V.

●

CS: Same voltage level as VREG

●

CX: Same voltage level as VREG

●

OUT: Same voltage level as VDD

The CS and CX pins have ESD protection diodes connected to VREG, therefore voltage

levels higher than VREG should not be used on CS and CX.

A level shifter that follows the VREG voltage of the STM8T141 should be used to

communicate with the STM8T141 at the correct voltages,

The only time that a voltage higher than VREG may be used on CS and CX is during option

programming when VREG is tied to VDD.

Note:

1

For in-circuit programming: make sure that no external components will influence the

voltage swing of the CS, CX and OUT pins.

2

For in-circuit programming: an external voltage regulator on the product may clip the VDD

voltage at its regulation voltage and prevent VDD from reaching the required option

programming voltage of 6.7 V. Large capacitors on VDD or VREG can increase the time

needed for the programmer to reach 6.7 V - sometimes the option programming instruction

might be given before the required voltage has been reached. Adjust all timing delays

accordingly.

3

The user documentation of the programming tool must contain the maximum load current

permitted to drive the application without disturbing the programming signals.

Table 1.

Voltages for reading or programming

VDD pin

Min

Typ

Max

Units

Programming mode entry

2.9

5.0

5.5

V

Option byte programming

6.6

6.7

6.8

Option byte reading

2.9

5.0

5.5