CHAPTER 19 IEBus CONTROLLER (V850/SB2)
User’s Manual U13850EJ4V0UM
477
(12)IEBus communication count register (CCR)
The IEBus communication count register (CCR) indicates the number of remaining bytes in the
communication byte number specified in the communication mode.
Bits 7 to 0 of the IEBus communication count register (CCR) indicate the number of transfer bytes.
This register reads the count value of the counter that is preset to the maximum number of transmitted bytes
(32 bytes) per frame specified in mode 1. Whereas SCR (IEBus communication success counter) is
decremented during normal communication (ACK), CCR is decremented when 1 byte has been
communicated, regardless of whether ACK or NACK.When the count value has reached “00H”, the frame end
flag (ENDFRAM) is set.
The maximum number of transfer bytes of the preset value of mode 1 per frame is 20H (32 bytes).
Figure 19-27. IEBus Communication Count Register (CCR) Format
After reset: 20H
R
Address: FFFFF3F6H
7
6
5
4
3
2
1
0
CCR
(13)IEBus clock selection register (IECLK)
This register selects the clock of IEBus. The main clock frequencies that can be used are shown below.
Main clock frequencies other than the following cannot be used.
•
6.0 MHz/6.291 MHz
•
12.0 MHz/12.582 MHz
Figure 19-28. IEBus Clock Selection Register (IECLK) Format
After reset: 00H
R/W
Address: FFFFF3F8H
7
6
5
4
3
2
1
0
IECLK
0
0
0
0
0
0
0
IECS
IECS
IEBus clock selection
0
@ f
XX
= 6.0 MHz or f
XX
= 6.291 MHz
1
@ f
XX
= 12.0 MHz or f
XX
= 12.582 MHz