Maple Systems MAP450D - Manual (Page 10)

Software Handshaking
Software handshaking, which uses the XON/XOff format, is available only in Interactive
mode. The following rules apply:
1. When the host controller sends an XOFF control code (hexadecimal 13), the OIT
halts transmission of any data to the host controller until the host controller sends an
XON control code (hexadecimal 11). While transmission is halted, each OIT keypress
continues to be displayed on the OIT but no data is transmitted to the host controller.
Instead, each character is temporarily stored in an 8 byte ‘Handshake’ buffer. When
the handshake buffer is full, each OIT keypress causes the OIT to sound a warning
beep. The data continues to be displayed on the OIT but is not stored in the
Handshake buffer. Therefore, the host controller does not receive any data that is
entered when the handshake buffer is full.
2. When the host controller sends the XON control code, the OIT sends the contents of
the Handshake buffer to the host controller before proceeding normally.
3. The OIT has the option of sending the XOFF control code to the host controller if the
host controller is sending data to the OIT faster than the OIT can process it. When the
OIT sends the XOFF control code to the host controller, the OIT ignores any further
transmissions from the host controller until the OIT sends the XON control code. The
OIT has an internal buffer size of 200 characters. When the OIT’s buffer contains 170
characters, the OIT sends the XOFF control code. The OIT sends the XON control
code when the buffer is empty (the time required to empty the buffer varies according
to the baud rate but is approximately 150 msec.).
Hardware Handshaking
Hardware handshaking, which uses the CTS/RTS format, is available only in Interactive
and Block modes. The following rules apply:
1. When the host controller deasserts the CTS line, the OIT halts transmission of any
data to the host controller until the CTS line is reasserted. While transmission is
halted, each OIT keypress continues to be displayed on the OIT but no data is
transmitted to the host controller. Instead, each character is temporarily stored in an 8
byte ‘Handshake’ buffer. When the handshake buffer is full, each OIT keypress
causes the OIT to sound a warning beep. The data continues to be displayed on the
OIT but is not stored in the Handshake buffer. Therefore, the host controller does not
receive any data that is entered when the handshake buffer is full.
2. When the host controller reasserts the CTS line, the OIT sends the contents of the
Handshake buffer to the host controller before proceeding normally.
3. The OIT has the option of deasserting the RTS line if the host controller is sending
data to the OIT faster than the OIT can process it. When the OIT deasserts the RTS
line, the OIT ignores any further transmissions from the host controller until the OIT
reasserts the RTS line. The OIT has an internal buffer size of 200 characters. When
the OIT’s buffer contains 170 characters, the OIT deasserts the RTS line. The OIT
reasserts the RTS line when the buffer is empty (the time required to empty the buffer
varies according to the baud rate but is approximately 150 msec.).
No Handshaking
This setting disables any software or hardware handshaking. Although this is the easiest to
use, it is possible for the OIT to overwrite the host controller’s serial buffer, or vice versa.
9 MAP450D Operation Manual
1010-0101, Rev. 00