MicroWire Interface

MICROWIRE is a simple three-wire serial communications interface. This standard protocol handles serial communications between controller and peripheral devices. In this application note are some clarifications of MICROWIRE logical operation and of hardware and software considerations. A typical communication on the Microwire bus is made through the CS, SK, DI and DO signals.



A typical Microwire cycle starts by first selecting the device(bringing the CS signal high). Once the device is selected, a valid Start bit (“1”) should be issued to properly recognize the cycle. Following this, the 2-bit opcode of appropriate instruction should be issued. After the opcode bits, the 8-bit address information should be issued. For certain instructions, some (or all) of these 8 bits are don’t care values (can be “0” or “1”), but they should still be issued. Following the address information, depending on the instruction (WRITE and WRALL), 16-Bit data is issued. Otherwise, depending on the instruction (READ and PRREAD), the device starts to drive the output data on the DO line. Other instructions perform certain control functions and do not deal with data bits. The Microwire cycle ends when the CS signal is brought low. However during certain instructions, falling edge of the CS signal initiates an internal cycle (Programming), and the device

remains busy till the completion of the internal cycle.


1) Read and Sequential Read (READ)
2) Write Enable (WEN)
3) Write (WRITE)
4) Write All (WRALL)
5) Write Disable (WDS)

A Typical Interface diagram:

Microwire interface description 

Signal	Name	Description
DI	Serial data driven from interface	Input to uwire device
CS	Chips select driven from interface	Input to uwire device
SK	Serial clock driven from interface	Input to uwire device
DO	Serial data driven from uwire device	Input to uwire interface

Host interface description 

Signal	Description
µwire_hif_cs_ni	Active low chip select, this signal is for configuration Registers Access.
µwire_hif_rd_en_i	When asserted the data from the register addressed by the address bus will be kept on the bus read data bus after N clock cycle delay.
µwire_hif_wr_en_i	When asserted the data on the write data bus gets written to the register that matches with the address on the address bus in one/two clock cycle.
µwire_hif_addr_i [15:0]	Address to access different configuration registers of this core.
µwire_hif_wr_data_i [7:0]	Data to be written to the addressed register.
µwire_hif_rd_data_o [7:0]	Data read from the configuration register.Data becomes valid after latency of N Clocks.
µwire_hif_intr_o	This is interrupt line. This line will be high until all interrupts in  register  are read.

Host Interface Write cycle diagram 

Host Interface Read cycle diagram 

Configuration Registers :
1. Control Register
2. TDR_addr Register
3. TDR_data Register
4. Status Register
5. RDR Register
6. Revision Register

Operation command from processor
Read – 000
Write – 001
Write ALL – 010
Erase ALL – 011
Erase – 100
EWEN – 101
EWDS – 110

With this information , anyone can built the microwire ip from scratch for learning purpose.

There is serial to parallel data conversion and vice-versa. 

You will also get to know about the clock domain crossing. Define microwire read/write/etc cycles, observe the waveform and build your hardware.

Here is the link for top level micro-wire IP module in verilog.

microwire_top.v

Thanks. 

PS: Information provided here is for learning purpose only.