Atari ST series Technical Reference Manual page 44

Table 3-2. ucr Bits (continued)
Bit
7 Clock
0 = Use clock directly for transfer frequency (synchronous
transfer)
1 = Divide clock frequency by 16
The other input parameters control the Receive Status
Register (rsr), Transmit Status Register (tsr) and Synchronous
Character Register (scr). These need rarely be set by the user.
A value of — 1 in any of the input parameters will retain the
previous value for that parameter. For more complete infor­
mation on the MFP chip, see Appendix F.
The final character device configuration function con­
cerns the three input devices, the serial port, the MIDI port,
and the console keyboard. This function returns a pointer to
a data structure known as the I/O buffer record. The buffer
record contains a number of items of information about the
input buffer used by the device. The function, Iorec(), uses
the following syntax:
int dev;
long bufrec;
bufrec = Iorec(dev);
where dev specifies the devices whose buffer record will be
fetched. Possible device number include:
Device
Number Input Device
0 RS-232 serial port
1 Console (keyboard)
2 MIDI port
The address of the device's buffer record is returned in the
variable bufrec. The buffer record contains 14 bytes of data,
laid out as follows:
Table 3-3. bufrec Byte Values
Byte Element
Number Name
0 -3 ibuf
4 -5 ibufsize
6 -7 ibufhd
8 -9 ibuftl
10-11 ibuflow
12-13 ibufhi
* Explained below.
36
CHAPTER 3
Function
Contents
Address of the input buffer
Size of the input buffer (in bytes)
Index to head (next write position)
Index to tail (next read position)
Low water mark *
High water mark *