MAC7200 datasheet(223/976 Pages) FREESCALE

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External Signal Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

145

Figure 11-2 illustrates the state diagram for single pin MSEO transfers.

Note that the “End Message” state does not contain valid data on the MDO pins. Also, It is not possible to

have two consecutive “End Packet” messages. This implies the minimum packet size for a variable length

packet is 2x the number of MDO pins. This ensures that a false end of message state is not entered by

emitting two consecutive 1’s on the MSEO pin before the actual end of message.

Figure 11-3 illustrates the state diagram for two pin MSEO transfers.

The two-pin MSEO option is more efficient that the single pin option. Termination of the current message

may immediately be followed by the start of the next message on the consecutive clocks. An extra clock

to end the message is not necessary as with the one MSEO pin option. The two-pin option also allows for

consecutive “End Packet” states. This can be an advantage when small, variable sized packets are

transferred.

Table 11-15. MSEO Pin(s) Protocol

MSEO Function

Single MSEO data (serial)

Dual MSEO data

Start of message

1–1–0

11–00

End of message

0–1–1–(more 1’s)

00 (or 01)–11–(more 11’s)

End of variable length packet

0–1–0

00–01

Message transmission

0’s

00’s

Idle (no message)

1’s

11’s

Idle

Start

Message

Normal

Transfer

End

Message

MSEO=1

MSEO=0

MSEO=1

MSEO=0

MSEO=1

MDO: Invalid

Not Allowed

End

Packet

Figure 11-2. Single Pin MSEO Transfers

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