L9524C

Functional description

17/27

Each transmission frame consists of a beginning delimiter (one low bit) followed by the 8 bits

of the failure register beginning with bit 1. After the ending delimiter (one high bit) the

diagnostic output stage is inactive and is resistively pulled up to VVS.

The L9524C starts transmitting the first frame at the very first falling edge of the CI signal

after power-on. Since at that time the contents of the failure register are clear the first 9 bits

(beginning delimiter followed by the contents of the 8-bit failure register) which are

transmitted are always low. The L9524C repeats transmission of the frame every 32 falling

edges of the CI signal. Only during the time when the diagnostic output stage is inactive (i.e.

between the transmission of two frames) the contents of the failure register can be written.

Figure 7.

Serial diagnostic interface protocol

4.5

Current monitoring

The L9524C is able to monitor the current through 6 glow plugs by measuring the voltage

drop across sense resistors. Therefore, there are 4 positive sense input pins (SP1, SP2,

SP3, SP4) and 6 negative sense input pins (SN1, SN2, SN3, SN4, SN5, SN6). The sense

input pins must be connected to the sense resistors according to the following table:

contents of failure register

(all bits='low' at 1st frame)

contents of failure register

diagnostic

output

stage

inactive

first frame

frame

01

234

567

89

10 11

31

0

123

456

789

10

...

VVS

VCI

VCI off

VCI on

VDO

VVS

VDOL

t

t

t

...

...

...

Table 9.

Sense input pin connection

Sense resistor of glow plug

Positive sense input pin

Negative sense input pin

1SP1

SN1

2SP2

SN2

3SP3

SN3

4SP4

SN4

5SP2

SN5

6SP4

SN6