Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 44)

Section 4 General Programming
4.2
USER heap and issued without regard to controlling the receipt and
buffering of additional data.
When the serial input buffer requests one of the last 10 queues (1270
character locations left), it signals the serial host that it should stop sending
data. This is accomplished by either un-asserting the serial hardware
handshake RTS line or issuing an XOFF character (&h13), depending on
which serial handshake control has been switch selected. When more than
10 queues become available, it asserts RTS or issues an XON character
(&h11).
4.2.2 Log Buffer
The LOG buffer is similar to the serial output buffer. It can, under
program control, accept the data which would normally go to the serial
output buffer. It differs from the serial output buffer in that the data in the
LOG
buffer is maintained when the power is off. The LOG buffer is initially
allocated a 127 byte queue and, if required, acquires additional memory
from the USER heap. It retains these queues until ERASEd by the user
under program control.
4.2.3 Macro Buffers
MACRO queues are not allocated until a macro is defined. If a MACRO is
ERASE d, all the memory allocated to it is returned to the USER heap. The
MACRO text is stored into this queue exactly the way it was received from
the serial input. Syntax error checking is not performed when the MACRO is
created. If the length of the MACRO is longer than the 127 bytes allocated,
additional memory is allocated as required in 127 byte lengths. A single
MACRO
could be defined to consume the entire available USER heap.
When a MACRO is executed, a copy of the MACRO buffer is made and
placed at the start of the serial input buffer. If there is no available memory
in the USER heap, an OUT OF MEMORY error is generated which will cause
the front panel error LED to flash.