Epson S1C33L03 manual 515

VI SDRAM CONTROLLER BLOCK: SDRAM INTERFACE

A-1

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)

Synchronization

#BUSREQ

#BUSACK

Synchronization

					The external		bus
			S1C33	terminates	master controls				S1C33 controls
D[15:0]			the current bus cycle. 1 cycle 1 cycle		bus cycles.			1 cycle bus cycles.
						Hi-Z
A[23:0], #RD, #WR
SDRAM status			Self refresh			CMD		Self refresh
CKE (external device)	Hi-Z									Hi-Z
SDCKE (S1C33)						Hi-Z
						Hi-Z
SDRAM control (S1C33)	CMD		Self refresh						Self refresh
SDRAM control (external device)		Hi-Z		Self refresh		CMD		Self refresh		Hi-Z

Figure 2.17 Bus Release Procedure

B-VI

SDRAM

S1C33L03 FUNCTION PART EPSON B-VI-2-19