Motorola IH5 User Manual

Introduction

http://www.motorola.com/computer/literature

5-3

The 2155x SCRATCH7 register is used as the command/response register. 
In this register description and the following command descriptions, 
references to the upper half of the register refer to bits 0 through 15, and 
references to the lower half of the register refer to bits 16 through 31.

Format of command/response register (2155x SCRATCH7):

At reset, hardware clears this register. After reset, firmware writes this 
register with the value 0x80525354. This value indicates that a reset event 
has occurred and the interface is ready to accept commands.

Bit 0

The ownership flag (OWN). A value of 1 indicates the ‘host’ 
owns the register. A value of 0 indicates that the local cpu 
owns the register.

Bits 1 to 7

7 bit command opcode field. Each command is described in 
more detail in the following sections. 

Bit 8

Global error status flag (ERR). If the command completed 
successfully, then this bit will be written with the value 0 upon 
command completion. If the command fails, it will be written 
with the value 1. Additional command specific error status 
may be returned in other fields of the register.

0 1 2 3 4 5 6 7 8 9

1
0

1
1

1
2

1
3

1
4

1
5

1
6

1
7

1
8

1
9

2
0

2
1

2
2

2
3

2
4

2
5

2
6

2
7

2
8

2
9

3
0

3
1

O
W
N

Command opcode

E
R
R

Command Options Command Data/Result