MICRF405 datasheet(12/46 Pages) MICREL

12 / 46 page

Micrel

MICRF405

April 2006

M9999-041906

(408) 955-1690

Writing to n Registers having Non-Incremental

Addresses

Registers with non-incremental addresses can be

written to in one write-sequence as well. Example of

non-incremental addresses: “0,1,3”. However, this

requires more overhead, and the user should

consider the possibility to make a “continuous”

update, for example, by writing to “0,1,2,3” (writing

the present value of “2” into “2”). The simplest

firmware is achieved by always writing to all

registers. Refer to previous sections.

This write-sequence is divided into several sub-

parts:

• Disable the generation of load-signals by

clearing bit “load_en” (D0 in ControlRegister0)

• Repeat for each group of register having

incremental addresses:

Bring SEN active

Enter first address for this group, R/W bit and

values

Bring SEN inactive

• Finally, enable and make a load-signal by

setting “load_en”

Refer to the previous sections for how to write to 1 or

n (with incremental addresses) registers in the

MICRF405.

Reading from the Control Registers in MICRF405

The “read-sequence” is:

1. Enter address and R/W bit

2. Change direction of SIO line

3. Read out a number of octets and change SIO

direction back again.

It is possible to read all, 1 or n registers. The

address to read from (or the first address to read

from) can be any valid address (0-29). Reading is

not destructive, i.e., values are not changed. The

SIO line is output from the MICRF405 (input to user)

for a part of the read-sequence. Refer to procedure

description below.

A read-sequence is described for reading n

registers, where n is number 1-30.

SEN

SIO

SCK

Data read

from register

Internal load pulse

generated here

A6 A5 A4 A3 A2 A1 A0 R/W D7 D6D5 D4 D3 D2 D1 D0

SIO INPUT

SIO OUTPUT

SAMPLE TIME

Figure 4. Reading from a Control Register.

In Figure 4 above, 1 register is read. The address is

A6, A5, … A0. A6 = MSB. The data read out is D7,

D6, …D0. The value of the R/W bit is always “1” for

reading.

• Bring SEN low

• Enter address to read from (or the first address

to read from) (7 bits) and

• The R/W bit = 1 to enable reading

• Make the SIO line an input to the user (set pin in

tristate)

• Read n octets. The first rising edge of SLK will

set the SIO as an output from the MICRF405.

The 405 will change the SIO line at positive

edges of SCK. The user should read the SIO

line at the negative edges.

• Make the SIO line an output from the user again.

Reading from the Interrupt Register

If any of the interrupts, Vc_HI, Vc_LO or Low_Batt,

is set the SRV pin will go high. Read the interrupt

flagged. It is possible to read this register at all

times, for instance, to read the tuned VCO_FREQ

setting which is also stored at the same address.

When rising SEN after haveing read the register, the

internal load pulse will then clear all interrupt flags.

To keep the flags when reading it, it is therefore

necessary to set LOAD_en=0 before hand.

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