Power-Down Mode; Bus Release Procedure - Epson CMOS 32-Bit Single Chip Microcomputer S1C33L03 Technical Manual

Power-down Mode

The SDRAM controller supports three power-down modes for the S1C33 Core (HALT, HALT2, and SLEEP).
In HALT mode, the bus clock is not turned off. Therefore, this mode can be set at any time.
In HALT2 and SLEEP modes, the SDRAM's auto-refresh function is disabled. Therefore, the SDRAM must be
placed in self-refresh mode before entering HALT2 or SLEEP mode, by following the procedure described below.
1. Set SDRSRF (D5/0x39FFC1) to "1" in order to enable the SDRAM's self-refresh function.
2. Check to see that SDRSRM (D6/0x39FFCA) = "0" (i.e., SDRAM is being self-refreshed).
3. Execute the HALT or SLP instruction.
Because the OSC3 clock is required for the SDRAM controller to be able to operate, the SDRAM must also be
placed in self-refresh mode following the above procedure before switching the CPU clock to OSC1 or turning the
OSC3 clock off.
Note: Because the SDRAM is taken out of self-refresh mode when accessed, steps 2 and 3 of the above
procedure must be executed on other memory than SDRAMs.

Bus Release Procedure

When the CPU releases the external bus, all of the SDRAM signal input/output pins, except for BCLK output when
SDRCLK = "1", are placed in the high-impedance state or set for input mode. As a result, another device acting as
the bus master gains control of the SDRAM.
The following illustrates a procedure where control of the SDRAM is switched.
BCLK
INTX (external device)
#BUSREQ
#BUSACK
D[15:0]
A[23:0], #RD, #WR
SDRAM status
Hi-Z
CKE (external device)
SDCKE (S1C33)
SDRAM control (S1C33)
SDRAM control (external device)
S1C33L03 FUNCTION PART
S1C33 terminates
the current bus cycle.
Self refresh
CMD Self refresh
Hi-Z
Figure 2.17 Bus Release Procedure
EPSON
VI SDRAM CONTROLLER BLOCK: SDRAM INTERFACE
Synchronization
The external bus
master controls
1 cycle 1 cycle bus cycles.
Hi-Z
CMD
Hi-Z
Hi-Z
Self refresh CMD
Synchronization
S1C33 controls
1 cycle bus cycles.
Self refresh
Hi-Z
Self refresh
Hi-Z
Self refresh
B-VI-2-19
A-1
B-VI
SDRAM