diff --git a/go.mod b/go.mod
index 7760195..a67d62f 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/rolfl/modbus
 
 go 1.15
+
+require github.com/jessevdk/go-flags v1.4.0 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..1b3c118
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/jessevdk/go-flags v1.4.0 h1:4IU2WS7AumrZ/40jfhf4QVDMsQwqA7VEHozFRrGARJA=
+github.com/jessevdk/go-flags v1.4.0/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
diff --git a/mbcli/client.go b/mbcli/client.go
new file mode 100644
index 0000000..7085d05
--- /dev/null
+++ b/mbcli/client.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/rolfl/modbus"
+)
+
+var busses = make(map[string]modbus.Modbus)
+
+// 1200, 2400, 4800, 19200, 38400, 57600, and 115200.
+var bauds = map[string]int{
+	"1200":   1200,
+	"2400":   2400,
+	"4800":   4800,
+	"9600":   9600,
+	"19200":  19200,
+	"38400":  38400,
+	"57600":  57600,
+	"115200": 115200,
+}
+
+var parities = map[string]int{
+	"N": modbus.ParityNone,
+	"E": modbus.ParityEven,
+	"O": modbus.ParityOdd,
+}
+
+var stopbits = map[string]int{
+	"1": 1,
+	"2": 2,
+}
+
+func client(access string) (modbus.Client, error) {
+	parts := strings.Split(access, ":")
+	if parts[0] == "tcp" {
+		if len(parts) != 4 {
+			return nil, fmt.Errorf("expect exactly 4 parts for TCP client access tcp:host:port:unit - not: %v", access)
+		}
+		host := strings.Join(parts[1:3], ":")
+		unit, err := strconv.Atoi(parts[3])
+		if err != nil {
+			return nil, err
+		}
+		if _, ok := busses[host]; !ok {
+			mb, err := modbus.NewTCP(host)
+			if err != nil {
+				return nil, err
+			}
+			busses[host] = mb
+		}
+		return busses[host].GetClient(unit), nil
+	}
+	if parts[0] == "rtu" {
+		if len(parts) < 6 || len(parts) > 7 {
+			return nil, fmt.Errorf("expect exactly 4 parts for TCP client access rtu:device:baud:parity:stop:(dtr:)unit - not: %v", access)
+		}
+		device := parts[1]
+		baud, ok := bauds[parts[2]]
+		if !ok {
+			return nil, fmt.Errorf("illegal baud %v", parts[2])
+		}
+		parity, ok := parities[parts[3]]
+		if !ok {
+			return nil, fmt.Errorf("illegal parity %v", parts[3])
+		}
+		stop, ok := stopbits[parts[4]]
+		if !ok {
+			return nil, fmt.Errorf("illegal stop bits %v", parts[4])
+		}
+		dtr := false
+		if len(parts) == 7 {
+			if parts[5] != "dtr" {
+				return nil, fmt.Errorf("DTR must be specified as 'dtr', not %v", parts[5])
+			}
+		}
+		unit, err := strconv.Atoi(parts[len(parts)-1])
+		if err != nil {
+			return nil, err
+		}
+		key := fmt.Sprintf("%v:%v:%v:%v:%v", device, baud, parity, stop, dtr)
+		if _, ok = busses[key]; !ok {
+			mb, err := modbus.NewRTU(device, baud, parity, stop, dtr)
+			if err != nil {
+				return nil, err
+			}
+			busses[key] = mb
+		}
+		return busses[key].GetClient(unit), nil
+	}
+	return nil, fmt.Errorf("unknown modbus connection type %v (expect tcp or rtu)", parts[0])
+}
diff --git a/mbcli/coils.go b/mbcli/coils.go
new file mode 100644
index 0000000..d78936f
--- /dev/null
+++ b/mbcli/coils.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type CoilGetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		Addresses []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *CoilGetCommands) Execute(args []string) error {
+	return genericClientReads("coil", c.Units, c.Args.Addresses, c.Timeout)
+}
+
+type CoilSetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		AddressValues []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *CoilSetCommands) Execute(args []string) error {
+	initializeConnections(c.Units)
+
+	timeout := time.Second * time.Duration(c.Timeout)
+	addresses, err := addressValues(c.Args.AddressValues, false)
+	if err != nil {
+		return err
+	}
+
+	// run the commands
+	for _, sys := range c.Units {
+		client, _ := client(sys)
+		for _, rng := range addresses {
+			flags := make([]bool, len(rng.values))
+			for i, v := range rng.values {
+				flags[i] = v == 1
+			}
+			_, err := client.WriteMultipleCoils(rng.address, flags, timeout)
+			if err != nil {
+				fmt.Printf("Write Holdings: Failed: %v\n", err)
+				continue
+			}
+			got, err := client.ReadCoils(rng.address, len(flags), timeout)
+			if err != nil {
+				fmt.Printf("Write Holdings verify: Failed: %v\n", err)
+			} else {
+				fmt.Printf("Write Holdings verify: %v\n", got)
+			}
+		}
+	}
+	return nil
+}
+
+type CoilCommands struct {
+	Get CoilGetCommands `command:"get" alias:"read" description:"Get or read Coil values"`
+	Set CoilSetCommands `command:"set" alias:"write" description:"Set or write Coil values"`
+}
diff --git a/mbcli/diag.go b/mbcli/diag.go
new file mode 100644
index 0000000..513f6de
--- /dev/null
+++ b/mbcli/diag.go
@@ -0,0 +1,75 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/rolfl/modbus"
+)
+
+type DiagnosticCommands struct {
+	ServerID bool     `short:"s" long:"serverid" description:"Return the ServerID value"`
+	DeviceID bool     `short:"d" long:"deviceid" description:"Return the DeviceID values"`
+	Counts   bool     `short:"c" long:"counts" description:"Return the Diagnostic counter values"`
+	Events   bool     `short:"e" long:"events" description:"Return the Event counter value"`
+	Clear    bool     `short:"C" long:"clear" description:"Reset the Event counter value"`
+	Timeout  int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Units    []string `short:"u" long:"unit" description:"Unit(s) to contatc" required:"true"`
+}
+
+func (c *DiagnosticCommands) Execute(args []string) error {
+	// initialize the connections
+	for _, sys := range c.Units {
+		_, err := client(sys)
+		if err != nil {
+			return err
+		}
+	}
+
+	timeout := time.Second * time.Duration(c.Timeout)
+
+	// run the commands
+	for _, sys := range c.Units {
+		client, _ := client(sys)
+		if c.ServerID {
+			if sid, err := client.ServerID(timeout); err != nil {
+				fmt.Printf("ServerID: Failed: %v\n", err)
+			} else {
+				fmt.Printf("ServerID: %v\n", sid)
+			}
+		}
+		if c.DeviceID {
+			if did, err := client.DeviceIdentification(timeout); err != nil {
+				fmt.Printf("DeviceID: Failed: %v\n", err)
+			} else {
+				fmt.Printf("DeviceID: %v\n", did)
+			}
+		}
+		if c.Counts {
+			counts := []modbus.Diagnostic{
+				modbus.BusCommErrors,
+				modbus.BusExceptionErrors,
+				modbus.BusCharacterOverruns,
+				modbus.ServerMessages,
+				modbus.ServerNoResponses,
+				modbus.ServerNAKs,
+				modbus.ServerBusies,
+			}
+			for _, count := range counts {
+				if cnt, err := client.DiagnosticCount(count, timeout); err != nil {
+					fmt.Printf("Count %v: Failed: %v\n", count, err)
+				} else {
+					fmt.Printf("Count: %v\n", cnt)
+				}
+			}
+		}
+		if c.Clear {
+			if err := client.DiagnosticClear(timeout); err != nil {
+				fmt.Printf("Diagnostic Reset: Failed: %v\n", err)
+			} else {
+				fmt.Printf("Diagnostic counters reset\n")
+			}
+		}
+	}
+	return nil
+}
diff --git a/mbcli/discretes.go b/mbcli/discretes.go
new file mode 100644
index 0000000..1d92fbc
--- /dev/null
+++ b/mbcli/discretes.go
@@ -0,0 +1,17 @@
+package main
+
+type DiscreteGetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		Addresses []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *DiscreteGetCommands) Execute(args []string) error {
+	return genericClientReads("discrete", c.Units, c.Args.Addresses, c.Timeout)
+}
+
+type DiscreteCommands struct {
+	Get DiscreteGetCommands `command:"get" alias:"read" description:"Get or read Discrete values"`
+}
diff --git a/mbcli/helpers.go b/mbcli/helpers.go
new file mode 100644
index 0000000..64c8098
--- /dev/null
+++ b/mbcli/helpers.go
@@ -0,0 +1,127 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type addressedRange struct {
+	address int
+	count   int
+}
+
+func addressRanges(refs []string) ([]addressedRange, error) {
+	ret := []addressedRange{}
+	for _, ref := range refs {
+		parts := strings.Split(ref, ":")
+		add, err := strconv.Atoi(parts[0])
+		if err != nil {
+			return nil, err
+		}
+		cnt := 1
+		if len(parts) > 1 {
+			cnt, err = strconv.Atoi(parts[1])
+			if err != nil {
+				return nil, err
+			}
+		}
+		ret = append(ret, addressedRange{add, cnt})
+	}
+	return ret, nil
+}
+
+type addressedValues struct {
+	address int
+	values  []int
+}
+
+func addressValues(refs []string, isbool bool) ([]addressedValues, error) {
+	ret := []addressedValues{}
+	for _, ref := range refs {
+		parts := strings.Split(ref, ":")
+		add, err := strconv.Atoi(parts[0])
+		if err != nil {
+			return nil, err
+		}
+		vals := []int{}
+		for _, piece := range parts[1:] {
+			valstrs := strings.Split(piece, ",")
+			for _, sval := range valstrs {
+				val, err := strconv.Atoi(sval)
+				if err != nil {
+					if isbool && (sval == "t" || sval == "true" || sval == "on") {
+						val = 1
+					} else if isbool && (sval == "f" || sval == "false" || sval == "off") {
+						val = 0
+					} else {
+						return nil, err
+					}
+				}
+				if val < 0 {
+					return nil, fmt.Errorf("illegal value %v", sval)
+				}
+				if isbool && val > 1 {
+					return nil, fmt.Errorf("illegal bit value %v", sval)
+				}
+				vals = append(vals, val)
+			}
+		}
+		ret = append(ret, addressedValues{add, vals})
+	}
+	return ret, nil
+}
+
+func initializeConnections(units []string) error {
+	for _, sys := range units {
+		_, err := client(sys)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func genericClientReads(toget string, units []string, addressRefs []string, timeoutSec int) error {
+	// initialize the connections
+	initializeConnections(units)
+
+	timeout := time.Second * time.Duration(timeoutSec)
+	addresses, err := addressRanges(addressRefs)
+	if err != nil {
+		return err
+	}
+
+	// run the commands
+	for _, sys := range units {
+		client, _ := client(sys)
+		var got interface{}
+		var name string
+
+		for _, rng := range addresses {
+			switch toget {
+			case "discrete":
+				got, err = client.ReadDiscretes(rng.address, rng.count, timeout)
+				name = "Get Discretes"
+			case "coil":
+				got, err = client.ReadCoils(rng.address, rng.count, timeout)
+				name = "Get Coils"
+			case "input":
+				got, err = client.ReadInputs(rng.address, rng.count, timeout)
+				name = "Get Inputs"
+			case "holding":
+				got, err = client.ReadHoldings(rng.address, rng.count, timeout)
+				name = "Get Holding Registers"
+			default:
+				return fmt.Errorf("unknown read type %v", toget)
+			}
+			if err != nil {
+				fmt.Printf("%v: Failed: %v\n", name, err)
+			} else {
+				fmt.Printf("%v: %v\n", name, got)
+			}
+		}
+	}
+	return nil
+}
diff --git a/mbcli/holdings.go b/mbcli/holdings.go
new file mode 100644
index 0000000..0ec0ede
--- /dev/null
+++ b/mbcli/holdings.go
@@ -0,0 +1,60 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type HoldingGetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		Addresses []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *HoldingGetCommands) Execute(args []string) error {
+	return genericClientReads("holding", c.Units, c.Args.Addresses, c.Timeout)
+}
+
+type HoldingSetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		AddressValues []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *HoldingSetCommands) Execute(args []string) error {
+	initializeConnections(c.Units)
+
+	timeout := time.Second * time.Duration(c.Timeout)
+	addresses, err := addressValues(c.Args.AddressValues, false)
+	if err != nil {
+		return err
+	}
+
+	// run the commands
+	for _, sys := range c.Units {
+		client, _ := client(sys)
+		for _, rng := range addresses {
+			_, err := client.WriteMultipleHoldings(rng.address, rng.values, timeout)
+			if err != nil {
+				fmt.Printf("Write Holdings: Failed: %v\n", err)
+				continue
+			}
+			got, err := client.ReadHoldings(rng.address, len(rng.values), timeout)
+			if err != nil {
+				fmt.Printf("Write Holdings verify: Failed: %v\n", err)
+			} else {
+				fmt.Printf("Write Holdings verify: %v\n", got)
+			}
+		}
+	}
+	return nil
+}
+
+type HoldingCommands struct {
+	Get HoldingGetCommands `command:"get" alias:"read" description:"Get or read Holding values"`
+	Set HoldingSetCommands `command:"set" alias:"write" description:"Set or write Holding values"`
+}
diff --git a/mbcli/inputs.go b/mbcli/inputs.go
new file mode 100644
index 0000000..2e6c5c5
--- /dev/null
+++ b/mbcli/inputs.go
@@ -0,0 +1,17 @@
+package main
+
+type InputGetCommands struct {
+	Units   []string `short:"u" long:"unit" description:"Unit(s) to contact" required:"true"`
+	Timeout int      `short:"t" long:"timeout" default:"5" description:"Timeout (in seconds)"`
+	Args    struct {
+		Addresses []string `required:"1"`
+	} `positional-args:"yes" required:"yes"`
+}
+
+func (c *InputGetCommands) Execute(args []string) error {
+	return genericClientReads("input", c.Units, c.Args.Addresses, c.Timeout)
+}
+
+type InputCommands struct {
+	Get InputGetCommands `command:"get" alias:"read" description:"Get or read Input values"`
+}
diff --git a/mbcli/mbcli.go b/mbcli/mbcli.go
new file mode 100644
index 0000000..be2ce74
--- /dev/null
+++ b/mbcli/mbcli.go
@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/jessevdk/go-flags"
+)
+
+type CLICommand struct {
+	Verbose    bool               `long:"verbose" description:"Print API requests and responses"`
+	Diagnostic DiagnosticCommands `command:"diag" alias:"diagnostics" description:"Diagnostic functions"`
+	Discrete   DiscreteCommands   `command:"discrete" alias:"discretes" description:"Discrete functions"`
+	Coil       CoilCommands       `command:"coil" alias:"coils" description:"Coil functions"`
+	Input      InputCommands      `command:"input" alias:"inputs" description:"Input functions"`
+	Holding    HoldingCommands    `command:"holding" alias:"holdings" description:"Holding functions"`
+}
+
+func main() {
+	clicmd := CLICommand{}
+
+	parser := flags.NewParser(&clicmd, flags.HelpFlag|flags.PassDoubleDash)
+
+	_, err := parser.Parse()
+
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}