LM2502 datasheet(11/27 Pages) NSC

11 / 27 page

Functional Description (Continued)

OFF PHASE

In the OFF phase, both Master and Slave MPL transmitters

are turned off with zero current flowing on the MC and MD

lines. Figure 7 shows the transition of the MPL bus into the

OFF phase. If an MPL line is driven to a logical Low (high

current) when the OFF phase is entered it may temporarily

pass through as a logical High (low current) before reaching

the zero line current state.

The link may be powered down by asserting both the Mas-

ter’s and Slaves’s PD* input pins (Low). This causes the

devices to immediately put the link to the OFF Phase and

internally enter a low power state. To avoid loss of data the

Master’s PD* input should only be asserted after the MPL

bus has been in the IDLE state for at least 20 MC clock

cycles. This gives the Slave enough time to complete any

write operations received from the MPL bus.

CPU INTERFACE COMPATIBILITY

The CPU Interface mode provides compatibility between a

CPU Interface and a small form factor (SFF) Display or other

fixed I/O port application. Two options are allowed:

TABLE 4. Modes

Mode

Description

m68 Interface

(E, R/W*), 16-bit support

i80 Interface

(WR*, RD*), 16-bit support

It is not required that both the Master and the Slave to be

configured in the same mode. For example the Master may

be configured as an 80xx (i80) interface while the Slave is

configured for an 68xx (m68) interface.

Control information is carried over both MD lines. MD0 car-

ries the D0–7 data bits while MD1 the D8–15 data bits. See

Figure 8.

20093305

FIGURE 6. MPL Power Up Timing

20093306

FIGURE 7. MPL Power Down Timing

LM2502 Datasheet(PDF) 11 Page - National Semiconductor (TI)