UM0470 datasheet(14/37 Pages) STMICROELECTRONICS

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Single wire interface module (SWIM)

UM0470

14/37

3.9

Physical layer

During the communication, the SWIM pin will be in pseudo-open drain configuration. The

SWIM pin in the device is capable of sinking 8 mA when it drives the line to 0. The external

pull-up on the SWIM line should be sized in such a way that the maximum rise time tr of the

SWIM line should be less than 1 sampling period of the bit (which is 100 ns +/- 4 %).

Figure 10.

Timings on SWIM pin

Table 3.

SWIM pin characteristics

Parameter

Symbol

Generic

formula

Timings for HSI = 10 MHz

LSI = 32 to 64 kHz

Min

Max

Fall time on SWIM pin

TBD

50 ns

Rise time on SWIM pin

TBD

96 ns

Inter-bit time

(The time which SWIM pin

stays high between 2 bits)

tib

TBD

Inter-frame time

(Time between end of a

frame and the next one)

tif

TBD

Low time for a bit at 0

High speed: tb0

TBD

768 ns

832 ns

Low speed: tb0

TBD

1.6 µs

2.4 µs

Low time for a bit at 1

(High Speed)

High speed: Tb1

TBD

192 ns

208 ns

Low speed: Tb1

TBD

150 ns

250 ns

Injected current on SWIM

TBD

8 mA

tib

SWIM pin

tb0/tb1

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