Datasheet

Section 6 Bus Controller (BSC)
Page 312 of 1384 R01UH0310EJ0500 Rev. 5.00
Sep 25, 2012
H8S/2426, H8S/2426R, H8S/2424 Group
6.15 Usage Notes
6.15.1 External Bus Release Function and All-Module-Clocks-Stopped Mode
In this LSI, if the ACSE bit is set to 1 in MSTPCR, and then a SLEEP instruction is executed with
the setting for all peripheral module clocks to be stopped (MSTPCR = H'FFFF, EXMSTPCR =
H'FFFF) or for operation of the 8-bit timer module alone (MSTPCR = H'FFFE, EXMSTPCR =
H'FFFF), and a transition is made to the sleep state, the all-module-clocks-stopped mode is entered
in which the clock is also stopped for the bus controller and I/O ports. In this state, the external
bus release function is halted. To use the external bus release function in sleep mode, the ACSE
bit in MSTPCR must be cleared to 0. Conversely, if a SLEEP instruction to place the chip in all-
module-clocks-stopped mode is executed in the external bus released state, the transition to all-
module-clocks-stopped mode is deferred and performed until after the bus is recovered.
6.15.2 External Bus Release Function and Software Standby
In this LSI, internal bus master operation does not stop even while the bus is released, as long as
the program is running in on-chip ROM, etc., and no external access occurs. If a SLEEP
instruction to place the chip in software standby mode is executed while the external bus is
released, the transition to software standby mode is deferred and performed after the bus is
recovered.
Also, since clock oscillation halts in software standby mode, if BREQ goes low in this mode,
indicating an external bus release request, the request cannot be answered until the chip has
recovered from the software standby state.
6.15.3 External Bus Release Function and CBR Refreshing/Auto Refreshing
CBR refreshing*
1
/auto refreshing*
2
cannot be executed while the external bus is released. Setting
the BREQOE bit to 1 in BCR beforehand enables the BREQO signal to be output when a CBR
refresh*
1
/auto refresh*
2
request is issued.
Notes: 1. The auto refresh control function is not supported by the H8S/2426 Group and
H8S/2424 Group.
2. The CBR refreshing control is not supported by the 5-V version.