MAX17841B datasheet(13/33 Pages) MAXIM

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UART Operation

The UART is the subsystem that transmits messages to

the UART slave devices and receives them back. The

host uses SPI buffer transactions to store unencoded

outgoing messages in the transmit buffer and also to read

decoded incoming messages out of the receive buffer as

shown in Figure 10. Table 5showsthesizeandorganiza-

tion of the UART buffers.

UART Interrupts

There are 12 different UART events that can cause an

interrupt (refer to the Register Table for details). For each

event, there is a status bit, an enable bit, and a flag bit.

The status bit is the real-time status of the event and can only

be set or cleared by the UART. The enable bit determines

whether or not the event causes an interrupt. Interrupt flags

(exceptthePOR_Flag)areedge-triggeredinthattheyareset

only when the interrupt enable bit is true and the correspond-

ingstatusbittransitionsfromalogic-zerostatetologic-one

state. Interrupt flags can only be cleared by the host.

If the flag enable is set when its corresponding status bit

is true, the flag is not set until the status bit transitions

fromalogic-zerostatetoalogic-onestate.Iftheflagis

cleared when the corresponding status bit is true, the flag

does not set again until the status bit transitions from a

logic-zerostatetoalogic-onestate.

When any flag is true, the UART asserts the INT pin. All

flags must be cleared for the INT pin to be deasserted.

TheonlyexceptionisthePOR_Flag,whichhasnoeffect

on INT.

Table 5. UART Buffers

Figure 10. UART Data Flow

PARAMETER

TRANSMIT BUFFER

RECEIVE BUFFER

Organization

4 x 7 bytes

1 x 62 bytes

Size

28 bytes

62 bytes

Message Capacity

4 messages

Variable

HostAccess

Read and Write

ReadOnly

HOST

SPI

PORT

SLAVE

DEVICE(S)

RECEIVE

BUFFER

UART

DECODER

RECEIVER

TRANSMIT

BUFFER

FILL BYTE

GENERATOR

UART

ENCODER

TRANSMITTER

Maxim Integrated │ 13

MAX17841B

Automotive SPI Communication Interface (ASCI)

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