48
Sending Data
Section 4-3
4-3-2
DMA Data Transmission
It is possible to transmit data using DMA (Direct Memory Access) depending
on the model of ASCII Unit and the communications port used.
Note
At ports that are capable of DMA transmission, DMA transmission is enabled
or disabled in the DM Setup Area according to the following table.
For communications ports that do not transmit DMA data, the data is sent byte
by byte from memory to the communications port by the PRINT command.
This means that until the transmission is completed, the BASIC program is
stopped. For ports that do transmit DMA data, the PRINT command simply
provides the trigger, and the DMA controller processes the data transmission.
This allows the BASIC program to proceed to execute the next line, speeding
up processing. Therefore, use DMA transmission to speed up processing.
If DMA data transmission is enabled and the OPEN command is executed,
the RTS/CTS flow control and Xon/Xoff flow control settings will be enabled. If
CTS or Xon/Xoff flow control is enabled, DMA will be disabled. When flow
control settings are enabled and DMA data transmission is used, the trans-
mission must be completed using PRINT command.
The amount of DMA data that can be sent at one time is 255 bytes max.
To transmit data that is more than 255 bytes, write a program as follows:
Example
A$ = ..........: 200 bytes
B$ = ..........: 100 bytes
PRINT A$;B$
This example will transmits 300 bytes of data.
Note
DMA data transmission is a method of sending data directly to a communica-
tions port without using the MPU. Because this does not involve the MPU, the
ASCII Unit is able to continue executing the BASIC program as data is being
transmitted. Transmission of data is carried out by a dedicated circuit (the
DMA controller).
4-3-3
Transmission Control Signals
If the RTS signal is OFF when the PRINT# command is executed, RTS is
turned ON, and the processing will proceed as follows:
For OPEN Command with
CTS_ON, DSR_ON
If CTS and DSR are both ON, data will be transmitted. If DSR is OFF when
transmission starts, the BASIC indicator will flash slowly and the Unit will wait
to transmit data. If CTS turns OFF during data transmission, data transmis-
sion will stop and wait, and the BASIC indicator will flash slowly.
Model
C200H-ASC11
C200H-ASC21
C200H-ASC31
Port
Port #1
Port #2
Port #1
Port #2
Port #1
Port #2
Port #3
DMA
transmission
(See note.)
NO
YES
NO
YES
YES
YES
NO
Bits
Name
Setting (hex)
m + 2 bits 08 to 15
Port #1 DMA transmission
(C200H-ASC31 only)
00: DMA disabled (default)
5A: DMA enabled
m + 3 bits 08 to 15
Port #2 DMA transmission
(all models)
00: DMA disabled (default)
5A: DMA enabled
Summary of Contents for C200H-ASC11
Page 1: ...C200H ASC11 ASC21 ASC31 ASCII Units Operation Manual Revised June 2000...
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