MC68HC908EY16 Datasheet, PDF (151/278 Pages) Motorola, Inc – Microcontrollers

ESCI Arbiter
13.9 ESCI Arbiter
The ESCI module comprises an arbiter module designed to support software for communication tasks as
bus arbitration, baud rate recovery and break time detection. The arbiter module consists of an 9-bit
counter with 1-bit overflow and control logic. The CPU can control operation mode via the ESCI arbiter
control register (SCIACTL).
13.9.1 ESCI Arbiter Control Register
Address:
Read:
Write:
Reset:
$0018
Bit 7
6
5
ALOST
AM1
AM0
4
ACLK
3
2
1
AFIN
ARUN AROVFL
0
0
0
0
0
0
0
= Unimplemented
Figure 13-18. ESCI Arbiter Control Register (SCIACTL)
Bit 0
ARD8
0
AM1 and AM0 — Arbiter Mode Select Bits
As shown in Table 13-12, these read/write bits select the mode of the arbiter module. Reset clears
AM1 and AM0.
Table 13-12. ESCI Arbiter Selectable Modes
AM[1:0]
00
01
10
11
ESCI Arbiter Mode
Idle / counter reset
Bit time measurement
Bus arbitration
Reserved / do not use
ALOST — Arbitration Lost Flag
This read-only bit indicates loss of arbitration. Clear ALOST by writing a 0 to AM1. Reset clears
ALOST.
ACLK — Arbiter Counter Clock Select Bit
This read/write bit selects the arbiter counter clock source. Reset clears ACLK.
1 = Arbiter counter is clocked with one quarter of the ESCI input clock generated by the ESCI
prescaler.
0 = Arbiter counter is clocked with the bus clock divided by four
NOTE
For ACLK=1, the Arbiter input clock is driven from the ESCI prescaler. The
prescaler can be clocked by either the bus clock or CGMXCLK depending
on the state of the ESCIBDSRC bit in CONFIG2.
AFIN— Arbiter Bit Time Measurement Finish Flag
This read-only bit indicates bit time measurement has finished. Clear AFIN by writing any value to
SCIACTL. Reset clears AFIN.
1 = Bit time measurement has finished
0 = Bit time measurement not yet finished
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
Freescale Semiconductor
151