Toshiba TX49 TMPR4937, Manual

Page: 119 / 553

Chapter 7 External Bus Controller
7-19
Figure 7.3.14 Ready Input Timing (Write Cycle)
7.3.8 Clock Options
External devices connected to the external bus can use the SYSCLK signal as the clock. The
SYSCLK signal clock frequency can be set to one of the following divisions of the internal bus clock
(GBUSCLK): 1/1, 1/2, 1/3, 1/4. The ADDR[14:13] signal is used to set this frequency during reset, and
the setting is reflected in the SYSCLK Division Ratio field (CCFG.SYSSP) of the Chip Configuration
Register.
The operation reference clock frequency can be set to one of the following divisions of the internal
bus clock (GBUSCLK) for each channel independent of the SYSCLK signal clock frequency: 1/1, 1/2,
1/3, 1/4. The external signal of the External Bus Controller operates synchronous to this operation
clock. The Bus Speed field (EBCCRn.SP) of the External Bus Channel Control Register sets this
frequency.
Please set the same value as CCFG.SYSSP to EBCCRn.SP when the external device uses the
SYSCLK signal. If these two values do not match, then the channel, the operation reference clock, and
the SYSCLK signal will no longer be synchronous and will not operate properly.
SYSCLK
ADDR [19 : 0]
SWE * /BWE *
DATA [31 : 0]
ACK * /READY
( Input )
3 clocks
4 clocks
CE *
Acknowledge Ready
EBCCRn.PWT:WT=2
EBCCRn.SHWT=0
Start Ready
Check
3 clocks
SYSCLK
CE *
ADDR [19 : 0]
SWE * /BWE *
DATA [31
:
0]
ACK
*
/READY
(Input)
4 clocks
Acknowledge Ready
EBCCRn.PWT:WT=2
EBCCRn.SHWT=0