Cypress CY14B101P manual Read RTC Rdrtc Instruction, Burst Mode Read Instruction Timing

PRELIMINARYCY14B101P

Figure 11. Burst Mode Read Instruction Timing

CS

SCK

SI

SO

0	1		2	3	4	5	6	7	0	1	2	3	4	5	6	7		20	21	22	23	0	1	2	3	4	5	6	7	0		7	0	1	2	3	4	5	6	7
																	~~														~
																														~
		Op-Code														17-bit Address
0	0	0	0		0	0	1	1	0	0	0	0	0	0	0	A16		A3	A2	A1	A0
									MSB							~~				LSB
																								Data Byte 1												Data Byte N
																						D7	D6 D5 D4			D3 D2		D1 D0		D7 D0			D7	D6	D5 D4		D3 D2		D1 D0
																					MSB							LSB		~~		MSB							LSB

CS

SCK

SI

SO

Figure 12. Write Instruction Timing

0	1	2	3	4	5	6	7	0	1	2	3	4	5	6	7	20	21	22	23	0	1	2	3	4	5	6	7
															~~
			Op-Code												17-bit Address
0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	A16	A3	A2	A1	A0	D7	D6	D5	D4	D3	D2	D1	D0
								MSB							~ ~				LSB MSB					Data			LSB
													HI-Z

Figure 13. Burst Mode Write Instruction Timing

CS

SCK

SI

SO

0	1	2	3	4	5	6	7	0	1	2	3	4	5	6	7	20	21	22	23	0	1	2	3	4	5	6	7	0		7	0	1	2	3	4	5	6	7
															~~													~
																						Data Byte 1							~				Data Byte N
		Op-Code													17-bit Address													~~
															~ ~						D6 D5 D4											D6 D5		D4
0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	A16	A3	A2	A1 A0		D7				D3 D2		D1	D0 D7		D0		D7				D3 D2		D1	D0
								MSB											LSB MSB								LSB

HI-Z

READ RTC (RDRTC) Instruction

Read RTC (RDRTC) instruction allows the user to read the contents of RTC registers. Reading the RTC registers through the serial output (SO) pin requires the following sequence: After the CS line is pulled LOW to select a device, the RDRTC opcode is transmitted through the SI line followed by eight address bits for selecting the register. Any data on the SI line after the address bits is ignored. The data (D7-D0) at the specified address is then shifted out onto the SO line. RDRTC also allows burst mode read operation. When reading multiple bytes from RTC registers, the address rolls over to 0x00 after the last RTC register address (0x0F) is reached.

The R bit in RTC Flag register must be set to '1' before reading RTC time keeping registers to avoid reading transitional data. Modifying the RTC Flag registers requires a Write RTC cycle. The R bit must be cleared to '0' after completion of the read operation.

The easiest way to read RTC registers is to perform RDRTC in burst mode. The read may start from the first RTC register (0x00) and the CS must be held LOW to allow the data from all 16 RTC registers to be transmitted through the SO pin.

Note Read RTC instruction operates at a maximum clock frequency of 25 MHz.

Document #: 001-44109 Rev. *B Page 11 of 32

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