Software interface

PM0083

6/13

DocID018532 Rev 3

2.3

Read a byte from the STM8T143

Prerequisite: POUT = HIGH and CX must be configured as input on the programming tool

before calling the read procedure.

Note:

The STM8T143 always assumes by default that it will receive a byte. It only transmits a byte

if the previous command instructed it do so.

Table 4. Read procedure

Step

Action

Description

1.

Wait for CX = HIGH

Wait for device to pull CX high to indicate that it is ready to transmit.

2.

POUT = LOW

Pull POUT low as part of the handshaking protocol.

3.

Wait for CX = LOW

Check if device responds to handshake with a low signal.

4.

POUT = HIGH

Pull POUT high before clocking in the data from the device.

5.

Clock in data from

device (8 bits)

Clock in 8 data bits on CX at a clock frequency of 8.8 kHz on

POUT. (Clock on POUT is ten times faster than it was during

programming mode entry.) The most significant bit is received first.

Data on CX becomes valid some time after the clock on POUT

goes low and is valid by the time the clock goes high. The first

seven bits keep their status until the next falling edge on the clock,

but the last bit changes its state extremely quickly after receiving its

rising clock edge. Therefore it is advised to sample the data just

before the clock rising edge.