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M37641F8

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI ELECTRIC  

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MITSUBISHI MICROCOMPUTERS

7641 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

(1) Cycle Steal Transfer Mode

When the DMAC Channel x (x = 0, 1) Transfer Mode Selection Bit

(DxTMS) is set to “0”, the respective DMAC Channel x operates in

the cycle steal transfer mode.

When a request of the specified transfer factor is generated, the

selected channel transfers one byte of data from the address indi-

cated by the Source Register into the address indicated by the

Destination Register.

There are two kinds of DMA transfer triggers supported: hardware

transfer factor and software trigger. Hardware transfer factors can

be selected by the DMACx (x = 0, 1) Hardware Transfer Request

Factor Bit (DxHR). To only use the Interrupt Request Bit, the inter-

rupt can be disabled by setting its Interrupt Enable Bit of Interrupt

Control Register to “0”.

The DMA transfer request as a software trigger can be generated

by setting the DMA Channel x (x = 0, 1) Software Transfer Trigger

Bit (DxSWT) to “1”.

The Source Registers and Transfer Destination Registers can be

either decreased or increased by 1 after transfer completion by

setting bits 0 to 3 in the DMAC Channel x (x = 0, 1) Mode Regis-

ter. When the Transfer Count Register underflows, the Source

Registers and Destination Registers are reloaded from their

latches if the DMAC Register Reload Disable Bit (DRLDD) is “0”.

The Transfer Count Register value is reloaded after an underflow

regardless of DRLDD setting. At the same time, the DMAC Inter-

rupt Request Bit and the DMA Channel x (x = 0, 1) Count Register

Underflow Flag are set to “1”.

The DMAC Channel x Disable After Count Register Underflow En-

able Bit (DxDAUE) is “1”, the DMAC Channel x Enable Bit

(DxCEN) goes to “0” at an under flows of Transfer Count Register.

By setting the DMAC Channel x (x = 0, 1) Register Reload Bit

(DxRLD) to “1”, the Source Registers, Destination Registers, and

Transfer Count Registers can be updated to the values in their re-

spective latches.

When one signal among USB endpoint signals is selected as the

hardware transfer request factor, and DMAC Channel x (x = 0, 1)

USB and Master CPU Bus Interface Enable Bit (DxUMIE) is “1”;

transfer between the USB FIFO and the master CPU bus interface

input/output buffer can be performed effectively. This transfer

function is only valid in the cycle steal mode. To validate this func-

tion, the DMAC Channel x (x = 0, 1) USB and the Master CPU Bus

Interface Enable Bit (bit 5 of DxTR) must be set to “1”. The follow-

ing shows an example of a transfer using this function.

Packet Transfer from USB FIFO to Master

CPU Bus Interface Buffer

When the USB OUT_PKT_RDY is selected as the hardware trans-

fer request factor; if the USB OUT_PKT_RDY is “1” and the

master CPU bus interface output buffer is empty, the transfer re-

quest is generated and the transfer is initiated. The

OUT_PKT_RDY retains “1” and a transfer request is generated

each time the output buffer empties until all the data in the corre-

sponding endpoint FIFO has been transferred.

The transfer ends when the last byte in the USB receive packet is

transferred and the OUT_PKT_RDY flag goes to “0” (in the case

of AUTO_CLR bit = “1”).

Byte Transfer from USB FIFO to Master CPU

Bus Interface Buffer

When the USB Endpoint 1 OUT_FIFO_NOT_EMPTY is selected

as a hardware transfer request factor, if there is data in the USB

Endpoint 1 FIFO and the master CPU bus interface output buffer

is empty; a transfer request is generated and the transfer is initi-

ated. The transfer is performed by unit of one byte.

Transfer from Master CPU Bus Interface

Buffer to USB FIFO

When the USB Endpoint X (X = 1 to 4) IN_PKT_RDY

(IN_PKT_RDY = “0”) is selected as a hardware transfer request

factor, if there is data in the master CPU bus interface output

buffer and the data in the USB FIFO is within the specified packet

size, a transfer request is generated.

The DMA transfer is terminated when a command (A0 = “1”) is in-

put to the master CPU bus interface input buffer.

The timing chart for a cycle steal transfer caused by a hardware-

related transfer request and a software trigger are shown in Figure

33 and 34, respectively.

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