Omega 208H, DAQP-208, 308 user manual

5.2.1 Data FIFO Register (base + 0)

The data FIFO register is considered as the access port to the data FIFO, which holds up to 2048 data words from the A/D conversion results. The port is also used for programming the data FIFO thresholds, as explained later in this section.

Note: Although the data FIFO register is 8 bits wide, it is strongly recommended 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). Two consecutive bytes should be read from or written into the port each time it is accessed. The following table illustrates bit allocation.

Table 5-5. Data FIFO Register Bit Allocation

	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
LSB	D7	D6	D5	D4	D3	D2	D1	D0
MSB	D15	D14	D13	D12	D11	D10	D9	D8

5.2.1.1 Data FIFO Operation Modes

Depending on the mode of operation, the 16-bit word read from or written into the register has different meanings as shown in the following table.

Table 5-6. Data FIFO Operation Mode

Mod	Selection Bit	A/D	Acces	Operation
e			s
0	0, threshold	Idle	Read	Verify data FIFO threshold
			Write	Program data FIFO threshold
1	1, data FIFO	Idle	Read	Read data FIFO
			Write	Write data FIFO (diagnosis)
2	0, threshold	Run	Read	Verify data FIFO threshold
			Write	Not allowed
3	1, data FIFO	Run	Read	Read data FIFO
			Write	Not allowed

The “selection bit” is also called the “program/access” control bit, as defined in the auxiliary control register (base + 7). Mode 0 is the FIFO program mode, under which the two consecutive words (four bytes) written into the register address will set the almost full and

DAQP-208/208H/308 Users Manual 40