L9788 datasheet(184/264 Pages) STMICROELECTRONICS

184 / 264 page

Micro second channel (MSC) interface

L9788

184/264

DS12308 Rev 4

18.3

Upstream communication

The serial data output [DO] is the synchronous serial data signal of the upstream channel.

The polarity for [DO] is ‚normal polarity'- i.e. a low level bit at [DO] is stored in the µC as a

logic ‚0', and a high level bit at [DO] is stored in the µC as a logic ‚1'. The serial data output

is single-ended.

The frequency is derived from fCL by an internal divider to typ. fDO = fCL/32. It can be

adjusted via MSC to fDO = fCL/16... fCL/128. The time for a bit is TSDO = 1/fDO.

Each upstream frame consists of 16 bit:



1 start bit, always '0'



4-bit-upstream address field (A[0..3] with LSB first)



8 bit data upstream data field (D[0..7] with LSB first)



1 upstream parity bit (with even parity for the complete data frame)



2 fDO stop bit, always '1'.

There are 16 commands to perform read accesses.

All the read command READ-N Upstream Block are composed of 4 continued frames sent

to µC.

Within the execution of these read commands an upstream data frame is sent after the 2

stop bits of the prior upstream data frame and one additional interframe bit waiting time. If a

new read command is received while the up-stream communication is active, the 16 bit up-

stream on-going is completed and the new read command is canceled. At the end of the

upstream frame the latched flags contained in the register are cleared automatically, if the

frame is interrupted by new read command, flags will not be cleared. The time from the read

command to the first upstream frame of the answer is less than 100 µs.

Outside the upstream frame the DO output is high impedance

Figure 86. MSC upstream

GADG1312161239PS

Start

bit

Stop

bits

Start

bit

AAAA

DDDDDDDD

AAA

Active level

MSB

Up stream Frame (14 bits)

Total up stream frame field (16 bits)

PARITY BIT

INTERFRAME

Next up stream frame (16 bits)

Address

Data field (8 bits)

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