LM628 datasheet(7/24 Pages) NSC

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AC Electrical Characteristics (Continued)

Pinout Description

(See Connection Diagrams) Pin numbers for the 24-pin sur-

face mount package are indicated in parentheses.

Pin 1 (17), Index (IN) Input: Receives optional index pulse

from the encoder. Must be tied high if not used. The index

position is read when Pins 1, 2, and 3 are low.

Pins 2 and 3 (18 and 19), Encoder Signal (A, B) Inputs:

Receive the two-phase quadrature signals provided by the

incremental encoder. When the motor is rotating in the posi-

tive (“forward”) direction, the signal at Pin 2 leads the signal

at Pin 3 by 90 degrees. Note that the signals at Pins 2 and 3

must remain at each encoder state (See

Figure 9) for a mini-

mum of 8 clock periods in order to be recognized. Because

of a four-to-one resolution advantage gained by the method

of decoding the quadrature encoder signals, this corre-

sponds to a maximum encoder-state capture rate of 1.0 MHz

CLK = 8.0 MHz) or 750 kHz (fCLK = 6.0 MHz). For other

clock frequencies the encoder signals must also remain at

each state a minimum of 8 clock periods.

Pins 4 to 11 (20 to 24 and 2 to 4), Host I/O Port (D0 to D7):

Bi-directional data port which connects to host computer/

processor. Used for writing commands and data to the

LM628, and for reading the status byte and data from the

LM628, as controlled by CS (Pin 12), PS (Pin 16), RD (Pin

13), and WR (Pin 15).

Pin 12 (5), Chip Select (CS ) Input: Used to select the

LM628 for writing and reading operations.

Pin 13 (6), Read (RD ) Input: Used to read status and data.

Pin 14 (7), Ground (GND): Power-supply return pin.

Pin 15 (8), Write (WR ) Input: Used to write commands and

data.

Pin 16 (9), Port Select (PS ) Input: Used to select com-

mand or data port. Selects command port when low, data

port when high. The following modes are controlled by Pin

16:

Commands are written to the command port (Pin 16

low),

Status byte is read from command port (Pin 16 low), and

Data is written and read via the data port (Pin 16 high).

Pin 17 (10), Host Interrupt (HI) Output: This active-high

signal alerts the host (via a host interrupt service routine)

that an interrupt condition has occurred.

Pins 18 to 25, DAC Port (DAC0 to DAC7): Output port

which is used in three different modes:

LM628 (8-bit output mode): Outputs latched data to the

DAC. The MSB is Pin 18 and the LSB is Pin 25.

LM628 (12-bit output mode): Outputs two, multiplexed

6-bit words. The less-significant word is output first. The

MSB is on Pin 18 and the LSB is on Pin 23. Pin 24 is

used to demultiplex the words; Pin 24 is low for the

less-significant word. The positive-going edge of the sig-

nal on Pin 25 is used to strobe the output data.

Figure 8

shows the timing of the multiplexed signals.

LM629 (sign/magnitude outputs): Outputs a PWM sign

signal on Pin 18 (11 for surface mount), and a PWM

magnitude signal on Pin 19 (13 for surface mount). Pins

20 to 25 are not used in the LM629.

Figure 11 shows the

PWM output signal format.

Pin 26 (14), Clock (CLK) Input: Receives system clock.

Pin 27 (15), Reset (RST) Input: Active-low, positive-edge

triggered, resets the LM628 to the internal conditions shown

below. Note that the reset pulse must be logic low for a mini-

mum of 8 clock periods. Reset does the following:

Filter coefficient and trajectory parameters are zeroed.

Sets position error threshold to maximum value (7FFF

hex), and effectively executes command LPEI.

The SBPA/SBPR interrupt is masked (disabled).

The five other interrupts are unmasked (enabled).

Initializes current position to zero, or “home” position.

Sets derivative sampling interval to 2048/f

CLK or 256 µs

for an 8.0 MHz clock.

DAC port outputs 800 hex to “zero” a 12-bit DAC and

then reverts to 80 hex to “zero” an 8-bit DAC.

DS009219-9

FIGURE 7. Data Word Write Timing

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