L6238 datasheet(27/35 Pages) STMICROELECTRONICS

27 / 35 page

6.1 Description

The L6238 contains a powerful serial port that

may be optionally used to dramatically increase

the functionality of the controller without signifi-

cantly increasing the pin count. The serial port

serves two primary functions:

1. Receive Control Information

A total of 16 bits of control information can be pro-

grammed via the serial port, in addition to the ca-

pabilities provided by external pins. By duplicating

key serial port control functions at dedicated pins,

the L6238 will still provide sufficient motor control

for many applications, without the use of the se-

rial port.

2. Provide Status Information

Certain status information is available only via the

serial port, with additional information available at

dedicated pins.

6.2 Block Diagram

Figure 29 is a simplified block diagram of the

serial port. It consists of a 16-bit shift register, a

16-bit latch, and some control logic. The serial

port utilizes 5 pins to communicate with the out-

side world. They are:

Data I/O The data I/O pin enables 16 bits of data

to flow in as control or out as status information.

Read/Write This pin selects read or write mode.

Clock Used to shift data in or out of the serial

port.

Disable If multiple controllers are connected for

parallel operation, this signal can be used to se-

lect communication to a particular port. If the Se-

rial Port is not used, the PORT DISABLE pin

should be tied high.

Strobe The read operation is transparent. When

the strobe is high, the data on the status bus

flows through to the serial register. In a write op-

eration, the loading of the control bits into the par-

allel control latch is an edge-triggered operation

occurring on the rising edge of the strobe.

6.3 Functional Truth Table

Table 4 defines the states for the disable and

R/W functions. If the disable pin is asserted high,

the Data I/O pin is tristated to a High-Impedance

state. The R/W pin determines whether the Data

I/O pin is an input or an output.

The AC operating parameters of the serial port

are defined in the Electrical Specifications.

Table 4: Truth Table.

Dis

R/W

Function

Write to Serial Port (Data I/O = Input)

Read to Serial Port (Data I/O = Output)

Chip Disabled (Data I/O = Hi Z)

6.4 Timing Diagrams

Figure 29: Block Diagram.

L6238

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