Omega 208H, DAQP-208, 308 user manual Threshold to FIFO size

5.2.1.3 FIFO Flags

When reading the register under mode 1 or 3, the first available data byte from the data FIFO will be returned if it is not empty, otherwise the returned byte is not defined. The FIFO full flag will be cleared after the data FIFO register is read provided there are no more data bytes written into the FIFO by the A/D converter under mode 1 or 3. The same will happen to the FIFO almost full flag if the data bytes available in the FIFO are less than the almost full threshold. The FIFO empty flag will be set immediately after the last byte is read from the FIFO. FIFO size is measured in bytes and is 4096. Table 5-8 lists the FIFO flag status.

Table 5-8. Data FIFO Flag Status

Data bytes in FIFO	Empty	Almost Full	Full
0	True	False	False
1 to (Threshold - 1)	False	False	False
Threshold to (FIFO size - 1)	False	True	False
FIFO size (4096)	False	True	True

5.2.2 Scan List Queue Register (base + 1)

The Scan List Queue Register is considered the access port to the scan list queue which can hold up to 2048 entries (each has two bytes). Each entry specifies an analog input channel and it’s associated gain as well as other settings.

Note: Although the scan list queue register is 8 bits wide, it is required that the register be accessed as a 16-bit word to guarantee integrity. The low byte (LSB or the least significant byte) should always be accessed first, followed by the high byte (MSB or the most significant byte). The bit definition is explained in Table 5-9.

Table 5-9. Scan List Queue Entry Bit Definition

Bit	Byte	Definition	Explanation
15	MSB	Reserved	as 0
14	MSB	Analog input mode	1/0 : differential/single-ended
13-12	MSB	Internal gain selection	00/01/10/11 : 1/2/4/8
11	MSB	Not in use	don’t care
10-8	MSB	Internal channel selection	0000..1111 : channel 0..7
7	LSB	Starting channel mark	Set to ‘1’ for the 1st entry in the
6	LSB	Reserved	for expansion cards (SSH)
5-4	LSB	External gain selection	00/01/10/11 : 1/2/4/8
3-0	LSB	External channel selection	0000..1111 : channel 0..7

DAQP-208/208H/308 Users Manual 43